A nitrogen-doped graphene cathode for high-capacitance aluminum-ion hybrid supercapacitors

Abstract

It is extremely important to design and fabricate high capacitance and stable Coulombic efficiency capacitors for energy storage. Herein, nitrogen-doped graphene coated on flexible tantalum foil is developed as a cathode for aluminum-ion hybrid supercapacitors which are based on an ionic liquid electrolyte with 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl)/AlCl₃. The results demonstrate that the nitrogen-doped graphene cathode offers a high capacitance of 254 F g⁻¹, a Coulombic efficiency of ∼90% and a cycle life of 1000 at a current density of 0.3 A g⁻¹. Meanwhile, the nitrogen-doped graphene cathode shows a capacitance of ∼130 F g⁻¹, a Coulombic efficiency of almost 100% and a cycle life of 2000 at a higher current density of 2.0 A g⁻¹. Moreover, the energy storage mechanism of the nitrogen-doped graphene in the aluminum-ion hybrid supercapacitors, that is, the dominant electrical double-layer capacitance (the adsorption and desorption of AlCi₄⁻ on the surface), and the intercalation/deintercalation in the nitrogen doped graphene, are confirmed.