An Ultrastable Nonaqueous Potassium-Ion Hybrid Capacitor

Potassium-ion hybrid capacitors (PIHCs) show great potential in large-scale energy storage due to the advantages of electrochemical capacitors and potassium-ion batteries. However, their development remains at the preliminary stage and is mainly limited by the kinetic imbalance between the two electrodes. Herein, an architecture of NbSe 2 nanosheets embedded in N, Se co-doped carbon nanofibers (NbSe 2 /NSeCNFs) as flexible, free-standing, and binder-free anodes for PIHCs is reported. The NbSe 2 /NSeCNFs with hierarchically porous structure and N, Se co-doping afford highly efficient channels for fast transportation of potassium ions and electrons during repeated cycling process. Furthermore, excellent electrochemical reversibility of the NbSe 2 /NSeCNFs electrode is demonstrated through in situ XRD, in situ Raman, ex situ transmission electron microscopy and element mapping. Thus, PIHCs with the NbSe 2 /NSeCNFs anode and active carbon cathode achieve a high energy of 145 W h kg −1 at a current density of 50 mA g −1 , as well as an ultra-long cycle life of over 10 000 cycles at a high current density of 2 A g −1 . These results indicate that the assembled PIHCs display great potential for applications in the field of ultra-long cycling energy storage devices.