"Plains-Hills": A New Model to Design Biomass-Derived Carbon Electrode Materials for High-Performance Potassium Ion Hybrid Supercapacitors

Enhancing the pseudocapacitance of carbon electrodes by doping them with heteroatoms becomes one promising way for fabricating high energy density supercapacitors. Nevertheless, rich doping with heteroatoms often arouses an inevitable contradiction between pseudocapacitance and conductivity. In this paper, inspired by the surface structure of the lotus leaf, a novel "plains-hills" model of carbon structure is proposed to solve this problem. For achieving this plains-hills structure, CaCl2 is employed as both a complexing agent and an oxygen scavenger in Ca2+-biogels via host-guest complexation, resulting in an ultrathin carbon unstacked nanosheet ("plains" domain) with numerous protuberances ("hills" domain) by a facile one-step pyrolysis. The obtained plains-hills architecture containing the defectrich hills and the ordered plains achieves a harmonious coexistence of high pseudocapacitance and good conductivity in heteroatom-doped carbon materials. As expected, this kind of plains-hills carbon electrode exhibits a reversible capacity of 147.2 mAh g(-1) at 10 A g(-1) after 5000 cycles, leading to an obvious energy density enhancement of potassium ion hybrid supercapacitors.