Dielectric polymer grafted electrodes enhanced aqueous supercapacitors

Supercapacitors (SCs) have become increasingly important in electrical energy storage and delivery owing to their high power densities and long lifetimes. Aqueous SCs are promising for large-scale engineering applications because of their low cost and safety. However, the low operating voltage and low energy density of aqueous SCs severely limit their practical applications. In this study, a nanoscale dielectric layer is grafted onto a graphene electrode to achieve both a high operating voltage and enhanced capacitance. Compared with an SC without dielectric grafting, a dielectric-enhanced SC (DESC) shows a higher capacitance by 2200%. The mechanism of the capacitance enhancement can be attributed to three factors: the dielectric polarization, the ions desolvation by the dielectric, and the enhanced quantum capacitance from charge transfer and ion adsorption in the polymer molecules. In addition, a 2.5 V pouch DESC with a 1 M KCl electrolyte is confirmed to cycle up to 50,000 times with a capacitance retention of 87.5%. The DESC presents the optimal electrochemical properties after it is grafted with a 5 nm dielectric layer. This study provides new insights into the design of high-voltage and high-energy-density aqueous SCs.