3D porous reduced graphene oxide-coated zinc anodes for highly-stable aqueous zinc-ion capacitors via electrostatic spray deposition

Zinc-ion energy storage devices are inexpensive and safe, benefitting from the abundance of Zn metal and high chemical stability. However, their electrochemical performance is poor, owing to the unstable Zn stripping/plating process of the Zn metal anode and the occurrence of side reactions. In this study, 3D porous reduced graphene oxide-coated Zn (rGO@Zn) was prepared via electrostatic spray deposition (ESD) and used as an anode for aqueous hybrid Zn-ion capacitors (ZICs). ESD is a cost-effective one-step technique that affords excellent control over the deposition morphology. Coating 3D porous rGO with a large surface area on Zn foil, resulted in a low charge transfer resistance and small voltage hysteresis (44.5 mV) with a long cycle life of over 3000 h. Moreover, the energy density improved at high rates (25 Wh kg⁻¹ at 10,882 W kg⁻¹) in aqueous hybrid ZICs. In-situ synchrotron transmission X-ray microscopy and optical microscopy analyses revealed that the formation of dendrites was inhibited in the as-fabricated ZICs. Furthermore, the conductive rGO on the surface of the Zn anode stabilized the electric field during the Zn stripping/plating process, and the functional groups guided the Zn²⁺ deposition sites, resulting in uniform Zn deposition during cycling and improved electrochemical performance.