Disproportionation of Sodium Superoxide in Metal–Air Batteries

The sodium oxygen battery is a promising metal–air battery; however, the discharge process is not well understood and the major discharge product is still under debate. The discharge products determined the theoretical specific energy and electrochemical performance of the battery. Now it is demonstrated that NaO₂ spontaneously disproportionates to Na₂O₂, no matter whether it is dissolved in solution or stays on the surface. The behaviors of NaO₂ in solution and on the surface are different. Solvents play a crucial effect on the disproportionation of dissolved NaO₂ species, which is fast in low donor number (DN) solvents such as acetonitrile but sluggish in high DN solvents such as DMSO. In situ XRD results exhibited the different product growing processes in various solvents. Surface NaO₂ would slowly disproportionate to Na₂O₂ anyway, but this process is relatively slow compared to the time span of discharge process and it does not affect the major product on discharge.