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

Abstract

The unresolved debate on the active reaction interface of electrochemical oxidation of lithium peroxide (Li2 O2 ) prevents rational electrode and catalyst design for lithium-oxygen (Li-O2 ) 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 Li2 O2 particles with an Li2 16 O2 /electrode interface and an Li2 18 O2 /electrolyte interface were fabricated. Upon oxidation, 18 O2 was evolved for the first quarter of the charge capacity followed by 16 O2 . These observations unambiguously demonstrate that oxygen loss starts from the Li2 O2 /electrolyte interface instead of the Li2 O2 /electrode interface. The Li2 O2 particles are in continuous contact with the catalyst/electrode, explaining why the solid catalyst is effective in oxidizing solid Li2 O2 without losing contact.