Aqueous Metal–Oxygen Batteries

Metal–oxygen batteries, utilizing oxygen from the air as the cathode active material, combine the characteristics of metal-ion batteries and fuel cells. They offer advantages such as high energy density, stable discharge voltage, and low production costs, demonstrating broad prospects for applications. In recent years, lithium–oxygen (Li–O2) batteries using non-aqueous electrolytes have garnered significant attention as a representative of next-generation high-energy batteries. However, several limiting factors still exist in common organic Li–O2 batteries: (1) the relatively expensive price of metallic lithium; (2) the formation of lithium dendrites on the anode, which leads to decreased overall battery performance and potential safety issues such as short circuits; (3) the use of highly flammable organic electrolytes, which not only result in low coulombic efficiency and poor cycling performance but also pose environmental concerns; (4) the inability to operate stably in an open-air environment; and (5) the tendency of discharge product Li2O2 to undergo further oxidation reactions with carbon carriers when the charging voltage exceeds 3.5 V (vs. Li+/Li). Therefore, metal–oxygen batteries, primary or secondary, using aqueous electrolytes are emerging.