O, N-Codoped, Self-Activated, Holey Carbon Sheets for Low-Cost And High-Loading Zinc-Ion Supercapacitors

Low-cost and high-loading cathodes are crucial for practical application of zinc-ion supercapacitors (ZICs) but achieving optimal performance in high-loading electrodes faces challenges due to sluggish ion transport, increased resistance, and unstable structure. Guided by theoretical calculations, high-loading carbon cathodes based on holey activated carbon sheets (HACS) are fabricated from a carefully chosen molecule. A simple pyrolysis-leaching treatment transformed the molecule into HACS with large surface area, hierarchical porous structure, and electroactive oxygen/nitrogen dopants. When combined with an aqueous binder, the optimized HACS-based high-loading electrode (16.1 mg cm-2) exhibits high-capacitance (454 F g-1 ) and fast-rate (1 A g-1) characteristics under lean electrolyte (6.2 mu L mg-1). More impressively, HACS is dry-pressed into free-standing thick electrodes up to 35.4 mg cm-2 and corresponding practical ZIC under limited Zn and low N/P ratio demonstrates ultrahigh areal capacitance (9 F cm-2) and energy density (3.47 mWh cm-2). The outstanding performance can be attributed to fast ion transport enabled by through-plane pores of HACS, as well as abundant double-layer and redox-active surfaces from favorable heteroatom-doped porous nanosheets. With its cost-effectiveness, elemental abundance, and structural tunability, this molecular carbon strategy offers a platform for making self-activated carbon electrodes at the molecular level towards practical supercapacitors. Through DFT calculation, molecule selection, and carbon fabrication, this work reports low-cost and high-loading carbon electrodes exhibiting outstanding performance for zinc supercapacitors. The remarkable performance is attributed to the large surface area, hierarchically porous structure, electroactive oxygen/nitrogen dopants, and holey sheet morphology, which enables ample double-layer and Faradic-redox surfaces for ion storage, as well as low-tortuosity pathways towards fast ion transport.image