Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li O in a Liquid-Cell Li-O Microbattery by Scanning Transmission Electron Microscopy.

Operando scanning transmission electron microscopy observations of cathodic reactions in a liquid-cell Li-O microbattery in the presence of the redox mediator tetrathiafulvalene (TTF) in 1.0 m LiClO dissolved dimethyl sulfoxide electrolyte are reported. It is found that the TTF addition does not obviously affect the discharge reaction for the formation of a solid Li O phase. The coarsening of Li O nanoparticles occurs via both conventional Ostwald ripening and nonclassical crystallization by particle attachment. During charging, the oxidation reaction at significantly reduced charge potentials mainly takes place at Li O /electrolyte interfaces and has obvious correspondence with the oxidized TTF distributions in the electric fields of the charged electrode. This study provides direct evidence that TTF truly plays a role in promoting the decomposition of Li O as a soluble charge-transfer agent between the electrode and the Li O .