Edge-plane exposed n-doped carbon nanofibers toward fast k-ion adsorption/diffusion kinetics for k-ion capacitors

Abstract

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors (PIHCs). Exposing active sites is recognized as an ideal strategy to resolve this issue, but the corresponding material design is challenging. Herein, carbon nanofibers with abundant, exposed edge-plane active sites due to (002) orientation adjustment were developed by a molten salt-assisted procedure. Importantly, due to the radial (002) orientation with more active edge-plane sites to adsorb K and shorten the K diffusion distance, the obtained carbon nanofibers harvest improved K adsorption/diffusion kinetics. Meanwhile, theoretical calculations indicate that the synchronically introduced N-doped defects can also lower the diffusion barrier and enhance K adsorption kinetics. Ex situ characterizations and electrochemical studies prove the improved kinetics that significantly improve the K storage properties of the obtained carbon nanofibers. Hence, a high cycling capacity of 252.8 mAh g-1 at 100 mA g-1 after 500 cycles and rate capacity of 181.5 mAh g-1 at 1000 mA g-1 after 1200 cycles have been achieved. Remarkably, the as-developed PIHCs deliver an energy density of 170 Wh kg-1 over 1-4 V, along with capacity retention of 81.6% at 2000 mA g-1 after 10,000 cycles.