A Reachable Sodium-Oxygen Battery Based on Sodium Superoxide Chemistry

Sodium-oxygen (Na-O 2 ) batteries offer a great potential to provide high energy density storage systems needed for small-sized and inexpensive electric vehicles owing to the abundance of sodium compared with lithium. Yet, their development is hindered by the low cycle life and poor energy efficiencies due to (i) the formation of singlet oxygen, resulting in parasitic reactions with the air cathode and the organic electrolyte, (ii) the formation of unstable SEI layers and dendrites associated with the metallic sodium anode, and (iii) lack of an active, stable cathode catalyst to reduce the overpotentials and improve the cycle stability. Here, we have developed a Na-O 2 battery cell composed of a highly active cathode catalyst that works well in synergy with an ether-based ionic-liquid electrolyte with specific redox mediators to act as co-catalysts to reversibly form and decompose sodium superoxide (NaO 2 ) via surface-mediated pathway at a low polarization gap of about 40 mV at a capacity of 1000 mAh/g. Different electrochemical and physicochemical characterization techniques, i.e., Raman spectroscopy, XRD, XPS, DEMS, SEM, and TEM were used to understand the cell chemistry. Moreover, a chemically synthesized Na anode protection layer implemented in this battery cell enabled a long cycle life of 900 with all-time energy efficiencies more than 80%, exceeding state-of-art Na-O 2 and Na-air batteries. The outcome of our study reveals the significance of the proper cell components design in Na-O 2 battery technologies as a promising venue in energy conversion and storage systems.