Nitrogen‐Doped Accordion‐Like Soft Carbon Anodes with Exposed Hierarchical Pores for Advanced Potassium‐Ion Hybrid Capacitors

Soft carbon (SC) is a promising anode material for potassium‐ion hybrid capacitors (PIHCs), but there are limited K + storage sites in common SC due to a skin‐like carbon film covering on the surface. To address this issue, a simple oxidization method to completely remove the skin‐like carbon film is reported and a novel accordion‐like architecture of SC (ASC) is constructed with a hierarchical porous framework composed of micropores, mesopores, and macropores, all of which can be exposed to K + electrolytes for enhanced energy storage. Importantly, this exposed structure facilitates pseudocapacitance modification by electro‐deposition of highly electrochemically active nitrogen‐doped graphene quantum dots (N‐GQDs) to enhance kinetic performance and additional K + storage. After annealing treatment to regulate N‐doping type, the accordion‐like N‐GQD@ASC‐500 exhibits excellent reversible capacity of 360 mAh g −1 as well as superior rate capability and cycle stability. Kinetic, in situ Raman/electrochemical impedance spectroscopy analysis, and density functional theory calculation elucidate the K + storage mechanism. As expected, the PIHC assembled with N‐GQD@ASC‐500 anode and porous carbon cathode delivers an ultrahigh energy/power density (171 Wh kg −1 and 20 000 W kg −1 ) with long cycle life. This work suggests that ASC is a promising anode material for designing of high‐performance PIHCs.