Oxygen Redox Versus Oxygen Evolution in Aqueous Electrolytes: Critical Influence of Transition Metals

Abstract Aqueous lithium‐ion batteries are promising electrochemical energy storage devices owing to their sustainable nature, low cost, high level of safety, and environmental benignity. The recent development of a high‐salt‐concentration strategy for aqueous electrolytes, which significantly expands their electrochemical potential window, has created attractive opportunities to explore high‐performance electrode materials for aqueous lithium‐ion batteries. This study evaluates the compatibility of large‐capacity oxygen‐redox cathodes with hydrate‐melt electrolytes. Using conventional oxygen‐redox cathode materials (Li₂RuO₃, Li_1.2Ni_0.13Co_0.13Mn_0.54O₂, and Li_1.2Ni_0.2Mn_0.6O₂), it is determined that avoiding the use of transition metals with high catalytic activity for the oxygen evolution reaction is the key to ensuring the stable progress of the oxygen redox reaction in concentrated aqueous electrolytes.