Multi-heteroatom doped nanocarbons for high performance double carbon potassium ion capacitor

Potassium-ion capacitor (KICs) is an emerging technology that can potentially combines the virtue of high power capability of supercapacitors and high energy density of batteries. Herein, we have scientifically transformed blue denim textile waste into two different forms of nanocarbons to assemble dual carbon potassium-ion hybrid capacitor (KIHC). The unique composition of indigo and sulphur dyes in blue jeans enables to produce multi-heteroatom (nitrogen, sulphur and oxygen) doped hard carbon (MHC) with large interlayer spacing (0.41 nm) in a single step. An in-situ transmission electron microscopy (TEM) analysis reveal that the charge stored in disordered and large interlayer spaced graphitic structure enable fast kinetics for efficient potassium-ion transportation. Coupling with an activated carbon foam (ACF)-based cathode, a full cell of potassium-ion capacitor successfully delivers a high energy density of 181 Wh kg−1 at 70.4 W kg−1 and 61.8 Wh kg−1 at 4000 W kg−1, as well as an long lifespan of 5000 cycles with over 89% of capacity retention. These performance statistics match or exceed state-of-the-art values for KIHCs, providing novel strategy to develop dual carbon ion capacitors with high energy and high power capabilities.