Electrochemical Oxidation of Li₂O₂ Surface-Doped with Li₂CO₃

Electrochemical oxidation of Li2O2, i.e., the charging reaction of the aprotic lithium-oxygen batteries (Li-O-2 batteries), is significantly influenced by its surface chemistry. Here, the surface species of Li2CO3, widely identified together with Li2O2 at the end of discharge, is investigated to understand its implication for the oxidation of Li2O2. In situ doping Li2O2 with various amounts of Li2CO3 has been obtained by reacting with CO2 gas in a controlled way, and the electrochemical oxidation of the doped Li2O2 is studied with a quantitative differential electrochemical mass spectrometer (DEMS). Instead of a single charging potential plateau and one O-2 gas evolution stage for the pristine Li2O2, Li2CO3-doped Li2O2 exhibits two O-2/CO2 gas evolution stages and three charging plateaus characterized with the larger overpotential for the initial and final stages. The conductivity of Li2CO3 dopant is invoked to explain the different oxidation behaviors of Li2CO3-doped Li2O2. The DEMS study of the electrochemical oxidation of isotope-labeled (Li2CO3)-C-13 is also conducted to identify the origins of O-2 and CO2 evolution during the oxidation of Li2CO3-doped Li2O2. The results reported here provide an improved understanding of the Li2O2 oxidation in the presence of parasitic Li2CO3 species and will contribute to the future development of Li-O-2 batteries.