Low‐Temperature Carbonized Nitrogen‐Doped Hard Carbon Nanofiber Toward High‐Performance Sodium‐Ion Capacitors

Carbon nanofiber (CNF) was widely utilized in the field of electrochemical energy storage due to its superiority of conductivity and mechanics. However, CNF was generally prepared at relatively high temperature. Herein, nitrogen‐doped hard carbon nanofibers (NHCNFs) were prepared by a low‐temperature carbonization treatment assisted with electrospinning technology. Density functional theory analysis elucidates the incorporation of nitrogen heteroatoms with various chemical states into carbon matrix would significantly alter the total electronic configurations, leading to the robust adsorption and efficient diffusion of Na atoms on electrode interface. The obtained material carbonized at 600 °C (NHCNF‐600) presented a reversible specific capacity of 191.0 mAh g −1 and no capacity decay after 200 cycles at 1 A g −1 . It was found that the sodium‐intercalated degree had a correlation with the electrochemical impedance. A sodium‐intercalated potential of 0.2 V was adopted to lower the electrochemical impedance. The constructed sodium‐ion capacitor with activated carbon cathode and presodiated NHCNF‐600 anode can present an energy power density of 82.1 Wh kg −1 and a power density of 7.0 kW kg −1 .