Porous Carbon Tubes Constructing Freestanding Flexible Electrodes for Symmetric Potassium-Ion Hybrid Capacitors

Developing electrode materials to apply in anodes and cathodes with superior kinetics and high specific capacity still remains a serious challenge for potassium-ion hybrid capacitors (PIHCs). Herein, a well-designed flexible freestanding electrode consisting of porous carbon tubes (FSF-PCTs) that functioned as both an anode and a cathode for PIHCs presents favorable energy storage performance. Based on this fully carbon-based FSF-PCTs electrode, symmetrical freestanding potassium-ion hybrid capacitors (SPIHCs) are developed. Moreover, SPIHCs deliver good practical application in terms of a high power density of 8109.9 W kg –1 (at 39.2 W h kg –1 ), a high energy density of 117.8 W h kg –1 (at 450 W kg –1 ), and a great cycle stability of 51 W h kg –1 at 1 A g –1 after 1500 cycles as well as ultrafast charge and slow discharge characteristics (full charge in only 1 min and the discharge time lasting for 15 min). Moreover, systematic characterization analysis in half potassium-ion batteries (PIBs) reveals that the K + storage mechanism in anode FSF-PCTs is a synergistic effect of intercalation and surface capacitance, and the operating principle of FSF-PCTs as a cathode is an adsorption behavior of PF 6 – on its surface.