Oxygen/fluorine-functionalized flexible carbon electrodes for high-performance and anti-self-discharge Zn-ion hybrid capacitors

Zn-ion hybrid capacitors (ZHCs) are considered promising electrochemical energy storage devices for flexible/wearable electronics. However, the unsatisfactory Zn2+ ions energy storage capability of current carbon electrodes seriously restricts its development. Herein, we effectively increase the electrochemical active surface area (also introducing pores) of the carbon nanotube (CNT) fiber bundles electrode and simultaneously introduce oxygen/fluorine functional groups with abundant C–OH and semi-ionic C–F bonds on the CNT fiber bundles electrode for facilitating the chemical adsorption of Zn2+ ions to produce pseudo-capacitance and enhance electrode kinetics, by adopting a simple electrochemical exfoliation and activation process in fluorine-containing solution. The prepared OFCNT-5 fiber bundles electrode achieves an ultrahigh areal capacitance of 1556.8 mF cm−2 (volumetric capacitance of 593.1 F cm−3), impressive long-cycling stability with capacity retention of 91.8% after 90,000 cycles. Moreover, the fiber-shaped Zn//OFCNT-5 device also delivers a high energy density of 553.53 μW h cm−2 (210.86 mW h cm−3), a high power density of 26.83 mW cm−2 (10.22 W cm−3), and outstanding anti-self-discharge capability. Our method also possesses a good universality and can extend to carbon cloth or carbon paper electrodes, and acts as one general strategy to design high performance of flexible carbon electrodes for ZHCs application.