Origins of Dendrite Formation in Sodium–Oxygen Batteries and Possible Countermeasures

One limiting phenomenon for the cycle life of metal-oxygen batteries is the growth of dendrites during metal plating (cell charging). For the relatively new sodium-oxygen cell, this subject has been scarcely investigated, until now. Therefore, dendrite formation is systematically investigated herein, with the aim of gaining a more detailed understanding of the underlying mechanisms and relevant control parameters. Electrochemical impedance spectroscopy, cycling experiments, and optical characterization techniques are applied in situ and ex situ; sodium dendrite growth is directly visualized, for the first time, by means of a tubular glass cell. The growth of instable surface morphologies is discussed from a theoretical perspective to comprehend the experimentally observed dendrite growth. Furthermore, countermeasures against issues with dendrites are discussed, with the aim of increasing the cycle life of sodium-oxygen batteries.