Identifying Reactive Sites and Transport Limitations of Oxygen Reactions in Aprotic Lithium-O-2 Batteries at the Stage of Sudden Death

摘要

Discharging of the aprotic Li-O-2 battery relies on the O-2 reduction reaction (ORR) forming solid Li2O2 in the positive electrode, which is often characterized by a sharp voltage drop (that is, sudden death) at the end of discharge, delivering a capacity far below its theoretical promise. Toward unlocking the energy capabilities of Li-O-2 batteries, it is crucial to have a fundamental understanding of the origin of sudden death in terms of reactive sites and transport limitations. Herein, a mechanistic study is presented on a model system of Au|Li2O2|Li+ electrolyte, in which the Au electrode was passivated with a thin Li2O2 film by discharging to the state of sudden death. Direct conductivity measurement of the Li2O2 film and in situ spectroscopic study of ORR using O-18(2) for passivation and O-16(2) for further discharging provide compelling evidence that ORR (and O-2 evolution reaction as well) occurs at the buried interface of Au|Li2O2 and is limited by electron instead of Li+ and O-2 transport.