High aspect ratio hierarchical carbon nanoplate/functionalized carbon nanotube scaffolds for scalable binder-free ultrafast-charging supercapacitors

Abstract

Binder-free supercapacitors are effective in achieving rapid charging/discharging capabilities, high power/energy density, and potentially reduced manufacturing costs. In this study, hierarchical carbon nanoplates (HCN) fabricated through the carbonization of high aspect ratio, polycrystalline metal-organic framework nanoplates. These HCN structures are then hybridized with functionalized carbon nanotube (FCNT) scaffolds and applied as electrodes using a scalable shear-coating method, eliminating the need for binders. The synergistic effects of these components result in the capacitance of 206 F/g at 0.8 A/g and 148.8 F/g at 8 A/g with a retention of 72 % in half-cell setups, and a full symmetric cell capacitance of 126 F/g at 4 A/g and 76 F/g at 40 A/g with a retention rate of 61 %. The power and energy densities of the full cell were measured to be 3880 W/kg and 16.2 Wh/Kg, surpassing the upper bound for electrochemical capacitors. The high rate capability and capacitance are attributed to the well-designed architecture of the electrodes and the benefits of the carbon components. Specifically, the high aspect ratio of the HCN with the hierarchical pore structure enhances the active surface area and charge transport properties. Additionally, the increased intermolecular interactions within the FCNT phase create entangled scaffolds, imparting both conductive pathways and mechanical stability. The binder-free nature of the electrodes, complemented by the presence of HCN spacers in the FCNT matrix, expands pores and promotes the transfer of ion species. Importantly, the viscoelastic properties of the HCN/FCNT slurry enable electrode fabrication in large areas by a scalable coating method.