Building a Reactive Armor Using S-Doped Graphene for Protecting Potassium Metal Anodes from Oxygen Crossover in K–O2 Batteries

Protecting alkali metals from oxygen crossover is a key unsolved challenge in metal–oxygen batteries. Herein, we report a new "reactive-armor strategy" by using freestanding three-dimensional sulfur (S)-doped graphene with bicontinuous pore channels for protecting potassium (K) anodes from the undesired oxygen crossover. X-ray photoelectron spectroscopy and Fourier-transform infrared results show that the S-dopants react with oxygen/superoxide species to form anionic sulfonate/sulfate that locally promotes the nucleation and growth of KO2. The resultant KO2 layer anchored on the graphene outer surface acts as a barrier layer that prevents oxygen from reaching the K metal surface. After 140 cycles (>550 h), the protected K metal anodes still maintain metallic luster with little accumulation of byproducts. We think the use of organosulfur to build a reactive armor can be applicable to other metal–oxygen batteries in suppressing the parasitic damage from oxygen crossover.