Large-scale vertical graphene on nickel foil as a binder-free electrode for high performance battery-like supercapacitor with an aqueous redox electrolyte

Due to the special three-dimensional structures and excellent physicochemical properties, vertical graphene (VG) has been extensively investigated as potential material for supercapacitors. However, achieving VG-based supercapacitors with high-energy density and high-power density is a still tremendous challenge. Here we attempt to synthesize large-scale VG films on flexible substrates and design a novel battery-like supercapacitor (BSCs) with the VG on Ni foil (VG@Ni) as a binder-free electrode operating in the KOH electrolyte with the redox additives of K3Fe(CN)6 and/or K4Fe(CN)6. The VG@Ni electrodes demonstrate an ultrahigh areal capacitance of 1453 mF cm-2 at 5 mA cm-2 in 1 M KOH electrolyte with adding 0.07 M K3Fe(CN)6 and 0.07 M K4Fe(CN)6, coulombic efficiency greater than 90%, and long-life cycling stability (capacitance retention is 99.3% after 20000 charge-discharge cycles). The BSCs, which are assembled with two identical VG@Ni electrodes, deliver the areal capacitance of 231 mF cm-2 with energy density of 32 mu Wh cm-2 and power density of 2498 mu W cm-2 at 1 mA cm-2. These outstanding performances can be ascribed to the special feature and excellent properties of VG materials, high electronic conductivity of binder-free VG@Ni electrode, faradaic properties of redox electrolyte, and synergistic effects between the VG film and redox electrolyte.

Automated summary

Vertical graphene (VG) has unique three-dimensional structures and excellent physicochemical properties, making it a promising material for supercapacitors. In this study, large-scale VG films were synthesized on flexible substrates, and a novel battery-like supercapacitor (BSCs) was designed using VG on Ni foil (VG@Ni) as a binder-free electrode in KOH electrolyte with redox additives. The VG@Ni electrodes exhibited high areal capacitance, coulombic efficiency, and cycling stability. The BSCs assembled with VG@Ni electrodes showed impressive areal capacitance, energy density, and power density, thanks to the special features and properties of VG materials, high electronic conductivity of the binder-free VG@Ni electrode, and synergistic effects with the redox electrolyte.