Super hydrophilic carbon fiber film for freestanding and flexible cathodes of zinc-ion hybrid supercapacitors

Abstract

The oxygen-enriched super hydrophilic porous carbon fibers film has been synthesized as cathodes of ZHSCs via a facile electrospinning and subsequent nitric acid-treatment process. The prefabricated ZHSCs has a super long-term cycle performance. In particular, this cathode can operate stably under high load, different bending angles and a quasi-solid-state device, which increases its practical application potential. • Oxygen functional groups can improve the performance of carbon cathode. • The zinc-ion hybrid supercapacitors (ZHSCs) provide an ultralong-term lifespan. • The reaction mechanism between Zn 2+ and oxygen functional groups is proposed. • The ZHSCs can operate stably under harsh conditions. Aqueous zinc-ion hybrid supercapacitors (ZHSCs) are considered as promising candidates for flexible wearable energy storage devices. The key challenge is to develop carbon cathodes with high hydrophilicity, good flexibility and cycle stability. This paper reports a facile route to synthesize flexible oxygen-enriched carbon fiber films with super-hydrophilic character. ZHSCs with such carbon fiber cathodes achieve excellent energy and power densities of 97.7 Wh kg −1 /9.9 kW kg −1 with a long-term cycling stability (retention rate of 81% after 50,000 cycles). According to experiment analysis and theoretical simulations, it is discovered that the oxygen-containing functional groups on carbon fibers not only significantly improve their wettability, but also greatly facilitate the chemical adsorption of zinc ions and result in the enhanced capacities. In addition, those cathodes can operate well and stably not only under a high load of 20 mg cm −2 and a bending of 180°, but also in a quasi-solid-state device, promising for wearable electronic applications.