Asymmetric supercapacitor featuring carbon nanotubes and nickel hydroxide grown on carbon fabric: A study of self-discharging characteristics

Technological advancement in portable electronic devices is often inhibited by the inadequate capacity of energy-storage devices. Asymmetric all-solid-state supercapacitors (ASSCs) can overcome energy-storage limitations of symmetric ASSCs by utilizing two different electrodes to extend the operating voltage window without decomposition of the electrolyte. Here, we report on the fabrication of carbon cloth (CC)/nickel hydroxide (Ni(OH)₂) and CC/carbon nanotubes (CNTs) electrodes, consisting of conformal nanoparticles of Ni(OH)₂ and nanostructured CNTs grown directly on the grooves and crests of carbon fibers, to provide additional active area for charge storage. The CC/Ni(OH)₂ electrodes display an exceptional specific capacitance (C_s) of 3987 F g⁻¹ and an areal capacitance (C_a) of 1248 mF cm⁻², whereas the CC/CNTs electrodes exhibit a C_s of 928 F g⁻¹ and C_a of 278 mF cm⁻². Furthermore, the asymmetric ASSCs employing CC/Ni(OH)₂ as an anode and CC/CNTs as a cathode, exhibit a C_s of 196 F g⁻¹ at a cell potential of 1.8 V, yielding an energy density of 132.7 Wh kg⁻¹. Moreover, the asymmetric ASSCs display improved low self-discharge behavior by charging it at an optimal current density and time. The results suggest that the asymmetric ASSCs are a low cost and efficient alternative in energy storage applications.