Hierarchical Porous Carbon Nanoﬁbers for Compatible Anode and Cathode of Potassium-Ion Hybrid Capacitor
The development of electrode materials with the capability of balancing kinetics and capacity between battery-type anode and capacitor-type cathode is still a grand challenge for potassium-ion hybrid capacitors (PIHCs). Herein, we report design and synthesis of phosphorus/nitrogen co-doped hierarchical porous carbon nanofibers (PN-HPCNFs) that feature desirable one dimensional (1D) structure and favorable electrochemical properties for PIHCs application. We demonstrate the as-prepared PN-HPCNFs present highly attractive performance in terms of capacity or capacitance and durability as both battery-type anode and capacitor-type cathode of PIHCs, which endows it with great potential for practical application in full PIHCs by delivering a high energy density of 191 Wh kg-1 and a high power output of 7560 W kg-1 as well as an ultralong lifespan (82.3% capacity retention after 8000 cycles). Systematic characterization analysis and first-principle calculations demonstrate that the hierarchical pores in 1D structure, heteroatom P/N co-doping, and enlarged interlayer graphite spacing in the APN-HPCNF contribute synergistically to the outstanding electrochemical performance for PIHCs.