Hierarchical porous carbon pellicles: Electrospinning synthesis and applications as anodes for sodium-ion batteries with an outstanding performance

N-doped hierarchically structured carbon pellicles (CZIF-8/PAN) were prepared from the carbonization of zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN) composite fibers which were fabricated by electrospinning technique. The resultant free-standing nanofiberic pellicles can be cut into membrane disks and directly used as anode materials without any binder and additive. As an anode for sodium-ion batteries (SIBs), the CZIF-8/PAN nanofiberic carbon pellicles showed superior reversible capacities of 186.2 mAh g−1 at high current density of 1.0 A g−1 and an excellent cyclic stability (93.5% remaining after 600 cycles) compared to other similar reported carbonaceous anode materials for SIBs. The improved electrochemical performance of CZIF-8/PAN carbon pellicles is mainly attributed to the hierarchical porous structures produced by introducing large ZIF-8 particles as a template, which greatly promotes the large sodium cation transportation and electron transfer rates due to the enlarged pores and increased contact area between the electrode and electrolyte. In addition, the enhanced electrochemical performance of CZIF-8/PAN nanofiberic anodes also benefits from the doping of nitrogen atoms which enhance the conductivity and increase the active sites.