Nanoconfined vanadium nitride in 3D porous reduced graphene oxide microspheres as high-capacity cathode for aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (ZIBs) are receiving considerable research highlights owing to their high safety and environment-friendliness. To implement this promising technology for grid-scale energy storage, effective cathode materials with high capacity, cycle stability, and electrochemical kinetics should be developed. Herein, the synthesis of uniquely structured porous VN-reduced graphene oxide composite (VN-rGO) microspheres through a facile spray pyrolysis process and their application as cathodes for ZIBs are introduced. The electrochemical reaction mechanism of VN-rGO microspheres with zinc ions is investigated through various in situ and ex situ analyses. During the initial charge process, VN phase transforms into the Zn3(OH)2V2O7·2H2O (ZVOH) phase. From the second cycle and on, the ZVOH phase undergoes zinc-ion ingress and egress processes. VN-rGO microspheres exhibit an unprecedented high capacity (809 mA h g−1 at 0.1 A g−1), high energy density (613 W h kg−1), and good rate capability (467 mA h g−1 at 2.0 A g−1). The cathode delivers a reversible capacity of 445 mA h g−1 after 400 cycles at 1.0 A g−1, which ascertains the robustness of the structure. The 3D porous rGO matrix to which VN nanocrystals are homogenously anchored accelerates the zinc-ion storage kinetics and endows the cathode with structural robustness.