Influence of Hydrocarbon and CO2 on the Reversibility of Li–O2 Chemistry Using In Situ Ambient Pressure X-ray Photoelectron Spectroscopy

Identifying fundamental barriers that hinder reversible lithium–oxygen (Li–O2) redox reaction is essential for developing efficient and long-lasting rechargeable Li–O2 batteries. Addressing these challenges is being limited by parasitic reactions in the carbon-based O2–electrode with aprotic electrolytes. Understanding the mechanisms of these parasitic reactions is hampered by the complexity that multiple and coupled parasitic reactions involving carbon, electrolytes, and Li–O2 reaction intermediates/products can occur simultaneously. In this work, we employed solid-state cells free of carbon and aprotic electrolytes to probe the influence of surface adventitious hydrocarbons and carbon dioxide (CO2) on the reversibility of the Li–O2 redox chemistry using in situ synchrotron-based ambient pressure X-ray photoelectron spectroscopy. Direct evidence was provided, for the first time, that surface hydrocarbons and CO2 irreversibly react with Li–O2 reaction intermediates/products such as Li2O2 and Li2O, forming carboxylate and carbonate-based species, which cannot be removed fully upon recharge. The slower Li2O2 oxidation kinetics was correlated with increasing coverage of surface carbonate/carboxylate species. Our work critically points out that materials design that mitigates the reactivity between Li–O2 reaction products and common impurities in the atmosphere is needed to achieve long cycle-life Li–O2 batteries.