Encapsulating hollow Fe3O4 in intertwined N-doped carbon nanofibers for high-performance supercapacitors and sodium-ion batteries

Abstract

As a promising electrode for energy storage, Fe3O4 has many intriguing advantages, such as a high specific capacity, low cost, low toxicity, wide potential window and environmental benignity. However, the multi-phase changes of iron oxide during the charge and discharge process can give rise to a sharp decrease in its capacity. In addition, the low conductivity of Fe3O4 may hinder the charge transfer and ion diffusion during redox process. In order to solve the above issues, this study mainly attempts to design a nanocomposite of Fe3O4 encapsulated in intertwined N-doped carbon nanofibers (CNFs) via using electrospinning and high-temperature calcination. The sealed structure can efficiently relieve the volume effect of Fe3O4 and raise the stability of electrodes. While a 3-dimensional interconnected conductive network composed of CNFs can increase the electroconductibility of electrodes. At the same time, the N-doping increases active sites on the surface of CNFs, providing more space for ions and charges storage. Herein, different amounts of Fe3O4 are encapsulated in N-doped CNFs (Fe3O4-CNFs). Fe3O4-CNFs with 40 % content of Fe3O4 (4Fe3O4-CNFs) deliver splendid electrochemical performances for all-solid-state supercapacitors and sodium-ion batteries. The specific capacitance of 4Fe3O4-CNFs supercapacitor is 184.5 F g−1 and maintains 86.2 % of initial capacity at 2 A g−1 after 5000 times. Furthermore, 4Fe3O4-CNFs as the anode for the half cell vs. Na+/Na demonstrate a splendid specific capacity of 628.1 mAh g−1 at 0.02 A g−1 and can maintain 358.1 mA h g−1 after cycling for 200 laps at 500 mA g−1. Therefore, 4Fe3O4-CNFs can be widely used in energy storage.