Implications of 4 e- Oxygen Reduction via Iodide Redox Mediation in Li-O2 Batteries

The nonaqueous lithium-oxygen (Li-O-2) electrochemistry has garnered significant attention because of its high theoretical specific energy compared to the state-of-the-art lithium-ion battery. The common active nonaqueous Li-O-2 battery cathode electrochemistry is the formation (discharge) and decomposition (charge) of lithium peroxide (Li2O2). Recent reports suggest that the introduction of lithium iodide (LiI) to an ether-based electrolyte containing water at impurity levels induces a 4 e(-) oxygen reduction reaction forming lithium hydroxide (LiOH) potentially mitigating instability issues related to typical Li2O2 formation. We provide quantitative analysis of the influence of LiI and H2O on the electrochemistry in a common Li-O-2 battery employing an ether-based electrolyte and a carbon cathode. We confirm, through numerous quantitative techniques, that the addition of LiI and H2O promotes efficient 4 e(-) oxygen reduction to LiOH on discharge, which is unexpected given that only 2 e(-) oxygen reduction is typically observed at undoped carbon electrodes. Unfortunately, LiOH is not reversibly oxidized to O-2 on charge, where instead a complicated mix of redox shuttling and side reactions is observed.