Singlet oxygen vs. triplet oxygen: functions of 2D-MoO3 catalysts in conquering catastrophic parasitic-reactions in lithium– and sodium–oxygen batteries

Abstract

Aprotic electrolyte alkali metal–oxygen batteries that possess a higher energy density than lithium-ion batteries stand out as the most promising next-generation environmentally-friendly energy source. Parasitic reactions caused by the singlet oxygen released from the superoxide disproportionation reactions, however, lead to catastrophic fading in the battery cycle life. We attempted to seek a probable catalyst surmounting this dilemma and finally discovered the 2D-MoO₃ nanosheet as an electrode-catalyst to handle the side reactions. Previous studies focused mainly on the influence of solvents on side reactions and neglected the catalyst, and hence, in this research an innovative mechanism of battery reaction occurring on the 2D-MoO₃ nanosheet in aprotic solvents was fully explored from both thermodynamic and kinetic prospects. It is interesting to find that the 2D-MoO₃ nanosheet plays different roles in preventing the production of singlet oxygen in lithium– and sodium–oxygen batteries. The 2D-MoO₃ nanosheet could also trigger the deep reduction of alkali-metal peroxides, which is considered to be an effective method to avoid parasitic reactions. This work may shed new light on future research into highly reversible and efficient alkali metal–oxygen batteries.