Rechargeable Aprotic Zinc–Oxygen Batteries with Reversible ZnO Formation on Cathodes

Mastering the redox reactions of oxygen-a naturally abundant and high-energy material-holds transformative potential to address the limitations in energy density, cost, and resource availability of current batteries. Despite their high energy density and cost-effectiveness, conventional aqueous zinc-oxygen (Zn-O₂) batteries were born with poor rechargeability. Critically, whether reversible oxygen electrochemistry can be established in aprotic Zn-based electrolytes remains an open question. Herein, we show that ZnO, traditionally regarded as an insulating byproduct, can be harnessed as an exclusive and reversible cathode product, hence opening access to a rechargeable Zn-O₂ battery chemistry. At the heart of this O₂/ZnO redox is the combined use of high-donicity aprotic electrolytes and Ru-based catalysts, which enables selective oxygen reduction to form a chemically inert (toward electrolytes) but defect-rich ZnO phase, whose oxygen vacancies promote low-polarization Zn─O bond breaking upon recharge to release O₂. The resulting reversibility of the oxygen cathode, coupled with stable Zn plating/stripping at the anode, ensures a prolonged cycle lifespan exceeding 1000 h for aprotic Zn-O₂ cells. A semi-solid pouch cell with an energy density of 120 Wh kg^-1 is further achieved using a high utilization-rate (40%) Zn anode. This work advances oxygen redox understanding and balances rechargeability with energy density in Zn batteries.