Porous carbon nanofibers derived from low‐softening‐point coal pitch towards all‐carbon potassium ion hybrid capacitors

Abstract Potassium ion hybrid capacitors (PIHC) have promising applications in medium and large‐scale energy storage systems due to their high energy/power density, abundant potassium resource and low cost. However, the slow kinetics of battery‐type anodes originating from the large‐size K + results in a mismatch between the two electrodes, rendering the modest energy density of PIHC. Herein, we first develop an electrospinning strategy to successfully synthesize fibrous precursor by using the HNO 3 pre‐oxidized low‐softening‐point coal pitch as the low‐cost raw material. With further carbonization or KOH activation, the two types of carbon nanofibers (CNF) are fabricated as anode and cathode materials, respectively, towards the dual‐carbon PIHC devices. Thanks to its three‐dimensional interconnected porous conducting network and large layer spacing, the resulted CNF anode material is endowed with high reversible capacities, excellent rate and long cycle stability. Meanwhile, the activated CNF cathode with a large surface area of 2169 m 2 ·g −1 exhibits excellent capacitive performance. A PIHC constructed with the two fibrous electrodes delivers an energy density of 110.0 Wh·kg −1 at 200.0 W kg −1 , along with a capacitance retention of 83.5% after 10,000 cycles at 1.0 A·g −1 . The contribution here provides a cost‐efficiency avenue and platform for advanced dual‐carbon PIHC.