Aluminum-Ion Asymmetric Supercapacitor Incorporating Carbon Nanotubes and an Ionic Liquid Electrolyte: Al/AlCl₃-[EMIm]Cl/CNTs

An aluminum-ion asymmetric supercapacitor was assembled utilizing a cathode made of multi-walled carbon nanotubes (MWCNTs) in an ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl)-based electrolyte. Two types of energy-storage mechanisms, that is, electrochemical double-layer capacitance (adsorption/desorption of AlCl₄ ⁻ on the surface) and limited intercalation pseudocapacitance (intercalation/deintercalation of AlCl₄ ⁻ in the graphite layer) at low current density, were observed and characterized. Meanwhile, the specific capacitance and cyclic stability of this supercapacitor were also evaluated by using galvanostatically charging–discharging. The result demonstrates that the specific capacitance decreases with increasing current density, which corresponds to the two types of energy-storage mechanisms of this device. The corresponding retention rate of this device after 3500 cycles at current density of 0.4 A g⁻¹ was 82.4 %, which shows good cyclic stability.