How to Control the Discharge Product in Sodium–Oxygen Batteries: Proposing New Pathways for Sodium Peroxide Formation

It is an unsolved problem how to steer between sodium superoxide and sodium peroxide as discharge products in sodium–oxygen batteries. Sodium peroxide yields a higher theoretical energy density; thus, it is preferred in view of maximized energy density. Three novel approaches to form sodium peroxide are presented: First, cells loaded with sodium superoxide are further discharged in argon, with the aim of reducing sodium superoxide to peroxide. Second, carbon nanotube electrodes preloaded with sodium peroxide are utilized. Third, sodium peroxide is dissolved in the electrolyte to enhance precipitation of solid sodium peroxide. Interestingly, all approaches yield sodium superoxide as a discharge product. Thus, it might not be possible to have high energy density sodium–oxygen batteries with sodium peroxide as the discharge product. However, potential pathways for peroxide formation during discharge have been excluded to help to find the true factors that govern the competition between superoxide and peroxide formation.