Troubleshooting the Limited Zn2+ Storage Performance of the Ag2V4O11 Cathode in Zinc Sulfate Electrolytes via Favorable Synergism with Reduced Graphene Oxides

A zinc-ion battery (ZIB) employing an aqueous electrolyte, that is, an aqueous zinc-ion battery (AZIB), represents a unique combination of high energy and high power with much-desired safety. In this respect, vanadium oxide-based cathodes, with open frameworks and rich valence states, have shown promising characteristics toward hosting the Zn2+ ions. Nevertheless, the degradation of the host during continuous (de-)intercalation and structural dissolution in the aqueous electrolyte affects the capacity and cycle life. Herein, we represent a high capacity and long cycle life AZIB based on an Ag2V4O11@reduced graphene oxide composite as a cathode in 1 M ZnSO4 electrolyte. We demonstrate the combined effect of the intercalation–displacement mechanism and partially irreversible formation of zinc hydroxyl sulfate as the charge storage mechanism in 1 M ZnSO4 electrolyte. We observed a comparatively quick capacity fading for the pristine Ag2V4O11; however, the capacity, rate capability, and cycle stability could be dramatically improved when the Ag2V4O11 was hydrothermally grown in situ in the presence of reduced graphene oxide (rGO). The charge storage mechanism, kinetics of charge storage, Zn2+ diffusion coefficient, effect of cycling on the phase/crystallinity, and morphology of the electrode materials were investigated. A morphological transformation from nanorod to ultrathin sheet/micro-belt-type Ag2V4O11 was observed with increasing rGO content. The rGO wrapped the Ag2V4O11 sheets/microbelts and thus reduced the charge transfer resistance and provided structural integrity during continuous cycling. The favorable synergism between the Ag2V4O11 and optimized rGO content could offer a high initial specific capacity of 328 mA h/g at 0.1 A/g, excellent rate capability with ∼150 mA h/g, specific capacity at 5 A/g, and long cycle stability with only 7% capacity loss over 3000 cycles.