Nitrogen doped three-dimensionally interconnected macroporous/mesoporous carbon nanofibers as free-standing electrode for room temperature sodium sulfur batteries

Abstract

High specific energy with low cost room temperature sodium‑sulfur (RT NaS) batteries have attracted much attention in the field of energy storage devices. The poor conductivity of the active material sulfur and its discharge products, the slow kinetics of the sodium‑sulfur redox reaction, the “shuttle effect” of sodium polysulfide and volume expansion effect during charging and discharging are the key scientific problems limiting its development. In this paper, the authors constructed a nitrogen doped three-dimensionally (3D) interconnected macroporous/mesoporous carbon nanofibers by electrospinning via selective etching SiO₂ nanospheres template. The as-prepared 3D nitrogen-doped porous carbon nanofibers (N-PCNF) act as free standing sulfur hosts for RT NaS batteries. The macroporous/mesoporous structure forms an interwoven carbon network that effectively improves the electronic conductivity and increases the accessibility of the electrolyte, thus facilitating rapid transfer of sodium ions and electrons. The mesoporous could prevent the shuttle phenomenon of sodium polysulfides. In addition, the heteroatom doped in the carbon matrix can not only improve the electrical conductivity but also anchor sulfur species to enhance the electrochemical performance. Consequently, the N-PCNF/S cathode exhibits an excellent initial capacity (866.9 mAh g⁻¹) at 0.5C, outstanding cycling performance (656.7 mAh g⁻¹ after 300 cycles at 0.5C), and high rate performance (405 mAh g⁻¹ at 2C). This study paves the way for the design macro-mesoporous heteroatom doped carbon material for the construction outstanding functional free-standing membrane and shines the light on the effective and feasible way for the inhibition of shuttle effect in RT NaS batteries.