Electrochemical\nOxidation of Li₂O₂ Surface-Doped with Li₂CO₃

Abstract

Electrochemical oxidation\nof Li₂O₂, i.e.,\nthe charging reaction of the aprotic lithium–oxygen batteries\n(Li–O₂ batteries), is significantly influenced by\nits surface chemistry. Here, the surface species of Li₂CO₃, widely identified together with Li₂O₂ at the end of discharge, is investigated to understand its\nimplication for the oxidation of Li₂O₂. In situ\ndoping Li₂O₂ with various amounts of Li₂CO₃ has been obtained by reacting with CO₂ gas in a controlled way, and the electrochemical oxidation of the\ndoped Li₂O₂ is studied with a quantitative differential\nelectrochemical mass spectrometer (DEMS). Instead of a single charging\npotential plateau and one O₂ gas evolution stage for the\npristine Li₂O₂, Li₂CO₃-doped Li₂O₂ exhibits two O₂/CO₂ gas evolution stages and three charging plateaus characterized\nwith the larger overpotential for the initial and final stages. The\nconductivity of Li₂CO₃ dopant is invoked to\nexplain the different oxidation behaviors of Li₂CO₃-doped Li₂O₂. The DEMS study of the\nelectrochemical oxidation of isotope-labeled Li₂¹³CO₃ is also conducted to identify the origins of O₂ and CO₂ evolution during the oxidation of Li₂CO₃-doped Li₂O₂. The results\nreported here provide an improved understanding of the Li₂O₂ oxidation in the presence of parasitic Li₂CO₃ species and will contribute to the future development\nof Li–O₂ batteries.