Operando Ambient Pressure X-ray Photoelectron Spectroscopy Studies of Sodium–Oxygen Redox Reactions

Lower charge overpotential of sodium–oxygen (Na–O 2 ) batteries makes them a promising electrical storage technology. However, they have an undesirable discharge product, sodium carbonate (Na 2 CO 3 ), which has widely been found in many previous studies. Whether and how the carbon components in the cathode are involved in the formation of Na 2 CO 3 is still not well understood. Herein, an all solid-state Na–O 2 battery was constructed and its charge and discharge cycles were studied using ambient pressure X-ray photoelectron spectroscopy. The operando XPS results clearly demonstrate the formation of Na 2 CO 3 on the cathode during the discharge cycle. A fraction of the carbonate formed can be cycled while charging the battery. Transformation of the carbon-based cathode to Na 2 CO 3 is a potential cause of capacity fading of the Na–O 2 battery.