Macroporous Vanadium Dioxide–reduced Graphene Oxide Microspheres: Cathode Material with Enhanced Electrochemical Kinetics for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are being extensively investigated owing to their safe operating conditions. Therefore, the search for cathode materials with optimum composition and nanostructure that enable high zinc-ion storage performance is underway. This study introduces a procedure for the formation of vanadium dioxide-nanoflake-reduced graphene oxide composite (P-VO2@rGO) microspheres with open pores through spray pyrolysis. Spherical cathode materials are formed by spray pyrolysis through the addition of polystyrene nanobeads and graphene oxide nanosheets in the spray solution. This enabled the formation of porous and crumpled graphene oxide microspheres, wherein thin VO2 nanoflakes are anchored. As a cathode for zinc-ion batteries, P-VO2@rGO exhibits a high rate capability (159 mA h g(-1); current density = 5.0 A g(-1)) and stable cycle performance for the 300 cycles at 1.0 A g(-1). To discern the synergistic effect of the reduced graphene oxide (rGO) and 3D-porous structure with a small crystal size on the zinc-ion storage, control samples (VO2-rGO composite and porous VO2 microspheres) are synthesized and tested as cathodes for zinc-ion batteries. The synergistic effect of compositing rGO and introducing porous structure with small crystal size enables high reversible capacity and enhances electrochemical kinetics of the electrode.