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 (Li 2 O 2 ). 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 Li 2 O 2 formation. We provide quantitative analysis of the influence of LiI and H 2 O 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 H 2 O 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.