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

Abstract

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 µL 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.