Clear Representation of Surface Pathway Reactions at Ag Nanowire Cathodes in All-Solid Li-O Batteries.

All-solid Li-O batteries have been constructed with Ag nanowire (AgNW) cathodes coated on Au-buffered garnet ceramic electrolytes and Li anodes on the other sides. Benefiting from the clean contacts of Li, e, and O on the AgNWs, the surface pathway reactions are demonstrated. Upon discharge, two types of LiO morphologies appear. The film-like LiO forms around the smooth surfaces of AgNWs, and hollow disk-like LiO forms at the joints in between the AgNWs as well as at the garnet/AgNW interfaces. The formation of films and hollow disks is in accordance with the process of O + Li + e → LiO and 2LiO → LiO + O, indicating that the disproportionation of LiO occurs at the solid interfaces. During the initial charge, decomposition occurs below the potential of 3.5 V, indicating the process of LiO → LiO + Li + e and LiO → Li + e + O rather than LiO → 2Li + 2e + O. The LiO decomposition starts at the AgNWs/LiO interfaces, causing the film-like LiO to shrink and the gas to release, followed by the collapse of hollow disk-like LiO. The results here clearly disclose the Li-O reaction mechanism at the all-solid interfaces, facilitating a deep understanding of key factors influencing the electrochemical performance of the solid-state Li-O batteries.