Carbon Nanotubes-Graphene-Solidlike Ionic Liquid Layer-Based Hybrid Electrode Material for High Performance Supercapacitor

Carbon nanomaterials are promissing electrode materials for supercapacitor applications due to their unique properties. Electrolyte accessibility is a big challenge in ionic liquid electrolyte-based supercapacitors with carbon nanomaterials as electrodes. In this study, an ultrahigh performance supercapacitor electrode, based on solidlike ionic liquid layer coated carbon nanotubes-hydrogen exfoliated graphene nanocomposite is demonstrated with hydrophobic ionic liquid as electrolyte. The presence of solidlike layers of ionic liquid is confirmed by structural and morphological analysis. The nanocomposite shows extremely high energy density (171 Wh/kg) and high specific capacitance (201 F/g) at a large specific current of 2 A/g, in terms of the mass of active electrode material, along with wide operating voltage (3.5 V). The Ragone fit shows that the time constant, maximum stored energy, and maximum available power are 0.575 s, 170.66 Wh/kg, and 148.43 kW/kg, respectively. The improvement in performance of the nanocomposite is mainly attributed to the presence of solidlike layers of ionic liquid on the surface of carbon nanomaterials, which effectively increases the electrolyte accessibility and number of shortest, directional ion transport paths. Here, carbon nanotubes play a role as a smart conductive spacer.