Empowered rechargeable solid-state Mg-O₂ battery using free-standing N-doped 3D nanoporous graphene

Rechargeable Mg-O₂ batteries (RMOBs) have emerged as promising next-generation energy storage systems owing to their high theoretical energy density, intrinsic safety, and low cost, as well as the high abundance of Mg resources. Herein, we develop a high-performance RMOB by employing three-dimensional N-doped nanoporous graphene—without the use of metal catalysts—as an air cathode to resist chlorination along with a mixed electrolyte composed of Mg(TFSI)₂ and MgCl₂ in diglyme to enhance the reversibility of the plating/stripping process on Mg anodes. The resulting RMOB achieves a high average discharge voltage of 1.21 V and remarkable cycling stability over 174 cycles at a fixed cut-off capacity of 1000 mAh·g⁻¹ per cycle. Furthermore, an all-solid-state highly flexible RMOB is assembled on the basis of the same design principles to deliver performance comparable to that of the liquid-based system. Ultimately, this study proposes a novel graphene-based durable air cathode and, thereby, a viable pathway toward advanced rechargeable Mg–air batteries.