Scalable waste-plastic-derived carbon nanosheets with high contents of inbuilt nitrogen/sulfur sites for high performance potassium-ion hybrid capacitors

Potassium-ion hybrid capacitors (KIHCs) demonstrate a broad prospect as promising electrochemical energy storage devices, attributing to combination merits of batteries and supercapacitors (i.e., high-energy density and high-power output). One pivotal task in the development of high-performance KIHCs is to search for an outstanding anode that can balance the kinetics mismatch between capacitor-type cathodes and battery-type anodes. As known that plastics seen commonly everywhere can have a high carbon content of 85.7 wt%. Herein, a large scalable carbon nanosheets (NPCNs) material with high contents of inbuilt nitrogen/sulfur sites is manufactured through a simple synthesis technique with low-cost waste plastic as precursors. The as-fabricated battery-type anode electrode suggests outstanding electrochemical performances owing to its expanded interlayer spacing, sufficient structural defects, functional groups, and redox-active sites favorable for improving the pseudocapacitive activity and accelerating the kinetics of K⁺ storage. In particular, a capacity retention rate of 94% over 16,000 long cycling, indicating unprecedented cycle stability. Moreover, in-situ Raman spectroscopy and density functional theory calculations further verify the potassium storage behavior. The as-assembled KIHCs deliver a remarkable energy/power density (61 Wh kg⁻¹ at 36576 W kg⁻¹) and ultralong cycling stability (87.0% capacity retention over 6000 cycles).