Energy-Dense Zinc Ion Hybrid Supercapacitors with S, N Dual-Doped Porous Carbon Nanocube Based Cathodes

Abstract

Zinc ion hybrid supercapacitors (ZIHSCs) are truly promising as next-generation high-performance energy storage systems because they could offer high energy density like batteries while exhibiting high power output and long cycle life traits of supercapacitors. The key point of constructing a high-performance ZIHSC is to couple the Zn anode with an appropriate cathode material, which has high theoretical capacity, cost-effectiveness, and intrinsic safety features. In this work, we have demonstrated the potentiality of S, N co-doped porous carbon nanocubes (S, N-CNCs) as a cathode material for devising a ZIHSC with excellent energy density and cycle life. The S, N-CNCs are prepared from a zeolitic imidazolate framework (ZIF)-8 precursor via a simultaneous pyrolyzing-doping strategy in an inert atmosphere. Resultant CNCs are monodisperse with an average size of around 65 nm and porous in nature, with uniform N and S doping throughout the structure. Benefitted from such hierarchical porous architecture and the presence of abundant heteroatoms, the assembled ZIHSC with S, N-CNC as the cathode and Zn-foil as the anode in a ZnSO₄ aqueous electrolyte could reach a specific capacity as high as 165.5 mA h g^-1 (331 F g^-1) at 1 A g^-1, which corresponds to a satisfactory energy density of 148.9 W h kg^-1 at the power density of 900 W kg^-1. The ZIHSC has displayed a good cycle stability with more than 70% capacity retention after 10,000 charge-discharge cycles. Furthermore, to verify the practical feasibility of such a cathode material, an aqueous 3D Zn@Cu//S, N-CNC full-cell device is fabricated, which has demonstrated a satisfactory specific capacity (49.6 mAh g^-1 at 0.25 A g^-1) and an impressive energy density (42.2 Wh kg^-1 with 212.2 W kg^-1). Full ZIHSC devices are also found to be efficient in powering light-emitting diodes, further substantiating their feasibility in next-generation energy storage applications.