Isotopic Labeling Reveals Active Reaction Interfaces for Electrochemical Oxidation of Lithium Peroxide.

The unresolved debate on the active reaction interface of electrochemical oxidation of lithium peroxide (Li O ) prevents rational electrode and catalyst design for lithium-oxygen (Li-O ) batteries. The reaction interface is studied by using isotope-labeling techniques combined with time-of-flight secondary ion mass spectrometry (ToF-SIMS) and on-line electrochemical mass spectroscopy (OEMS) under practical cell operation conditions. Isotopically labelled microsized Li O particles with an Li O /electrode interface and an Li O /electrolyte interface were fabricated. Upon oxidation, O was evolved for the first quarter of the charge capacity followed by O . These observations unambiguously demonstrate that oxygen loss starts from the Li O /electrolyte interface instead of the Li O /electrode interface. The Li O particles are in continuous contact with the catalyst/electrode, explaining why the solid catalyst is effective in oxidizing solid Li O without losing contact.