Nitrogen-enriched carbon nanofibers with tunable semi-ionic CF bonds as a stable long cycle anode for sodium-ion batteries

[Display omitted] •The modified electrospun fibers with semi-ionic CF bond was prepared by CF4 plasma.•The semi-ionic CF bond benefit to the fast ion and electron transfer for electrode.•Rate performance and long cycles of anode depend on the content of semi-ionic CF bond.•F doped N-enriched fibers deliver long term capacity with 150 mA h g−1 over 2000 cycles. The quest for getting more efficient carbonous anodes for sodium ion batteries (NIBs) prepared by simple and economical methods continues to be an important endeavor. Herein, a plasma-controlled method is developed for preparing semi-ionic CF bonds decorating nitrogen-enriched electrospinning carbon nanofibers (NCNFs) as a free-standing anode for NIBs. The semi-ionic CF bonds are beneficial to the fast ion and electron transfer for a free-standing electrode, which remarkably improves the rate performances of NCNFs as the NIBs anodes. The optimized sample delivers a reversible capacity of 199 mA h g−1 at 0.1 A g−1 and displays excellent long-term stability with reversible specific capacity around 150 mA h g−1 over 2000 cycles at 500 mA g−1 after the rate capability test. Moreover, the presence of semi-ionic CF bonds on plasma nitrogen-enriched electrospinning carbon nanofibers surfaces can reduce the resistance of the anode, thereby showing a more stable solid electrolyte interphase SEI) after electrochemical cycles.