In situ imaging of lithium superoxide dynamics in an all-solid-state Li–O2 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. [ABSTRACT FROM AUTHOR]