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From K-O2 to K-Air Batteries: Realizing Superoxide Batteries on the Basis of Dry Ambient Air.

Superoxide -based potassium-oxygen (K-O 2 ) batteries have demonstrated enormous potential to realize high-energy-density battery chemistry with low round-trip overpotentials . Although using air cathode is the ultimate goal to unlock the full potential of superoxide batteries, prior studies were limited to pure oxygen. Herein, we report the first K-air battery based on reversible superoxide electrochemistry . Spectroscopic and gas chromatography analyses are applied to evaluate the reactivity of KO 2 in ambient air. Despite that KO 2 reacts with water vapor and CO 2 to form KHCO 3 , it is found to be highly stable in dry air. With this knowledge, rechargeable K-air batteries were successfully demonstrated by employing dry air cathode. We further prove that the reduced partial pressure of oxygen plays a critical role in boosting the battery lifespan. With a more stable environment for K anode, a K-air battery delivers over 100 cycles (> 500 hours) with low round-trip overpotentials and high coulombic efficiencies as opposed to traditional K-O 2 battery that fails at an early stage. This work sheds light on the benefits and restrictions of employing air cathode in superoxide -based batteries, and will be of use for the development of practical metal-air batteries.