Web-in-web carbon cathode design unlocking high area capacitance and high-rate performance for Zn-ion hybrid supercapacitors

Abstract

Zn-ion hybrid supercapacitors (ZHSCs), as emerging energy storage systems, combine high energy and power density with cost-effectiveness and safety, attracting significant attention. However, due to the inherent energy storage mechanism and the diminishing marginal benefits of increased porosity on capacitance, engineering porous nanostructures to develop carbon materials with ideal architectures is crucial for achieving high performance. Herein, a novel web-in-web porous carbon/carbon nanotubes (CNTs) composite has been proposed, fabricated by a simple phase separation method and two-step carbonization. During pre-oxidation, gradual air oxidation induces the formation of an O, N co-doped polymer-chain template, which subsequently transforms into a graphitized web during high-temperature carbonization. The optimized web-in-web structure, enriched with abundant active sites, accelerates mass transport and charge transfer kinetics. When assembled in ZHSCs, the web-in-web cathode achieved a high area capacitance (14,309 mF cm⁻²) with high mass loading (38.2 mg cm⁻²). It delivered excellent high-rate performance at 50 mA cm⁻² with a capacitance retention of 83% after 10,000 cycles, also boosting a high energy density (1452.7 μWh cm⁻²) and power density (30.8 mW cm⁻²). Furthermore, ex situ characterization and in situ electrochemical analyses reveal hybrid energy storage mechanisms, involving both physical/chemical adsorption and precipitation/dissolution across different potential regions. This study provides a promising strategy for designing high-area-capacitance carbon cathodes boosting high-performance ZHSCs.