Toward a Sodium–“Air” Battery: Revealing the Critical Role of Humidity

Room temperature sodium–air batteries have a similar design and concept as lithium–air batteries. Using ambient air instead of pure oxygen as oxygen source is challenging because the minor components in air could lead to various side reactions and influence the electrochemical reaction route. Although water is an innegligible component in air, its impact on Li– and Na–air batteries is often underestimated. In this study, the electrochemical behavior of Na–air batteries under different relative humidity (RH) has been systemically investigated by galvanic cycling and cyclic voltammetry tests, as well as the identification of corresponding discharge products by physical characterizations such as XRD, FT-IR, and SEM. The reaction mechanisms of Na–air batteries under humid conditions are revealed and discussed. Na–air batteries suffer from more severe impact from the water content in air than Li–air batteries. NaOH and its derivatives are found to form and are proven to be fatal to the cells under humid ambience. Understanding the reaction mechanisms occurred in sodium air batteries under dry and humid ambient is critical to design and develop sodium–air batteries of high performance and long durability.