In situ imaging of lithium superoxide dynamics in an all-solid-state Li-O-2 nanobattery

Lithium superoxide (LiO2), which is considered to be an unstable intermediate, was shown recently to be a stable discharge product in lithium oxygen batteries (LOBs). As such, the in situ observation of LiO2 dynamics may provide direct evidence for the working mechanism of LOBs. Here we report in situ imaging of the nucleation, growth and stabilization of LiO2 in LOBs with Au nanoparticle coated carbon nanotubes as an air cathode by aberration corrected environmental transmission electron microscopy. During discharge, LiO2 spheres nucleated and grew from aggregated Li-Au alloy (Li15Au4) nanoparticle seeds and were stable for several minutes. Density functional theory calculations suggest that the de-activation of lithium via electron transfer from Li to Au and O weakens Li's electron donation capability and prevents the dissolution of superoxide-like species, which favors a one electron transfer oxygen reduction reaction, thus facilitating the nucleation and stabilization of LiO2. The lithium de-activation induced LiO2 dynamics advances our understanding of LiO2 mediated solid-state LOBs and may provide a new strategy for the design of LOBs.