High-performance supercapacitors based on defect-engineered carbon nanotubes

Defect-engineered carbon nanotubes (CNTs) were prepared by KOH activation and subsequent nitrogen doping. Controlled KOH activation of the CNTs enlarged the specific surface area to 988 m2 g−1, which is about 4.5 times greater than that of pristine CNTs. In addition, a hierarchical pore structure and a rough surface developed at high degrees of activation, which are advantageous features for fast ion diffusion. The subsequent nitrogen doping changed the band structure of the CNTs, resulting in improved electrical properties. Symmetric supercapacitors fabricated using these nitrogen-doped and activated CNTs (NA-CNTs) successfully worked across a wide potential range (0–3.5 V) and exhibited a high capacitance of 98 F g−1 at a current density of 1 A g−1. Furthermore, a low equivalent series resistance (2.2 Ω) was achieved owing to the tailored nanostructure and electrical properties of the electrode materials. Over the voltage range from 0 to 3.5 V, supercapacitors based on NA-CNTs exhibited a high specific energy of 59 Wh kg−1 and a specific power of 1750 W kg−1. In addition, a specific power of 52,500 W kg−1 with a 3-s charge/discharge rate was achieved with a specific energy of 26 Wh kg−1. Moreover, the supercapacitors showed stable performance over 10,000 charge/discharge cycles.