Water in Aprotic Li-O₂ Batteries: A Critical Review

The growing demand for more efficient technologies to store energy has brought us to a scenario where battery research is extremely important. Due to a higher energy density than lithium-ion batteries, lithium-oxygen batteries (Li-O2) have attracted attention with their theoretical energy density close to fossil fuels. However, much study is still needed to enable the practical use and production on a large scale of this technology, including the interference compounds present in atmospheric air, such as water. Advances in understanding the influence of water on aprotic Li-O2 batteries, catalysts used in conjunction with water, membranes to prevent corrosion at the anode, the influence of electrolyte solvent, and different mechanisms are summarized in this review. The addition of water can alter the cell capacity, charge and discharge overpotentials, and its cyclability. Studies on this subject are still at an early stage, and the role of water is still debatable in the literature. In this work we provide a thorough analysis from the reported data and create a framework to highlight the impacts of water in capacity, overpotentials, and cycling across many studies, looking for similarities between the systems and reaction mechanisms behind these phenomena. To better understand the mechanisms involved, simulation works that support theoretical equations and experimental results were used. Finally, the present work aims to synthesize data from several authors on a subject that is fundamental for the future use and production of Li-O2 batteries.