In Situ Electrochemical Tuning of MIL-88B(V)@rGO into Amorphous V2O5@rGO as Cathode for High-Performance Aqueous Zinc-Ion Battery

The design and fabrication of advanced cathode materials with excellent electrochemical properties to match the Zn anode is crucial for the development of aqueous zinc-ion batteries (ZIBs). Herein the synthesis of MIL-88B(V)@rGO composites is reported, in which MIL-88B(V) nanorods are anchored on reduced graphene oxide (rGO) sheets, as cathode for ZIBs, where the graphene oxide induces the formation of small-size nanorods instead of typical prism morphology. During the initial charge/discharge process, the cathode undergoes an in situ irreversible transformation from MIL-88B(V) to amorphous V 2 O 5 that acts as active site for the subsequent Zn 2+ insertion/extraction. The hierarchical structure of the composites and the amorphous V 2 O 5 provide abundant channels and active sites for Zn 2+ diffusion and adsorption. The density functional theory calculation reveals that the rGO sheets have two functions, i.e., to improve the conductivity and to reduce the Zn 2+ migration energy barrier. Consequently, the MIL-88B(V)@rGO cathode exhibits an ultrahigh reversible capacity of 479.6 mAh g −1 at 50 mA g −1 and good rate performance of 263.6 mAh g −1 at 5000 mA g −1 , which are superior to metal–organic frameworks (MOFs) cathodes reported in literature. This work may shed a new light to the design and fabrication of MOFs-based cathodes for aqueous ZIBs.