▎ 摘　　要

ABSTRACT: The electric double-layer capacitance (EDLC)based capacitor is hindered with low capacitance and low energy density. Here, in this report, we focused on the fabrication of a symmetric device having graphene as an EDLC electrode material and redox additive KI-integrated aqueous MgSO4 as an electrolyte. The high surface area of graphene was produced by annealing of graphene oxide in an inert atmosphere and confirmed through Xray photoelectron spectroscopy and Raman spectroscopy. The strategic 6% KI into MgSO4 delivered the highest specific capacitance with a wide working window of 0.7 V. Electrochemical measurements showed that graphene delivered a significantly greater specific capacitance (727.6 F/g) in a KI-integrated electrolyte (MgSO4 + KI) compared to 89.2 F/g in a MgSO4 electrolyte, owing to species such as IO3- and I3-(oxidation states of I). The symmetric device showed the maximum energy density (ED) of 69.3 Wh/kg, which can be achieved at the power density of 2.5 kW/kg, better than reported values in monovalent-based electrolyte devices. In this report, the charge storage mechanism, interactive association between Mg2+ ion insertion/extraction, and integration of redox KI had been comprehensively studied. The strategy shows a new path in the design of excellent ED capacitors without compromising the supercapacitor properties.