Electrospun heteroatoms-doped porous carbon nanofiber networks as free-standing and binder-free electrode for room temperature sodium sulfur batteries

Room temperature sodium-sulfur (RT Na-S) batteries are emerging as promising next generation energy storage technology due to the advantages of sodium and sulfur, including their abundant resources, low cost, and high theoretical specific capacity. However, their practical application is hindered by scientific challenges such as the poor electrical conductivity of sulfur and its discharge products, sluggish sodium-sulfur redox kinetic, the "shuttle effect" of sodium polysulfides, and volume expansion during cycling. In this study, we develop nitrogen-phosphorous co-doped carbon nanofiber (NP-PCNF) free-standing membrane via electrospinning, using triphenylphosphine (TPP) as phosphorus sources, to serve as sulfur host for RT Na-S batteries. The pores structure effectively mitigates volume expansion and facilitates the uniform deposition of discharge products during the sulfur redox reaction. Additionally, the three-dimensional non-woven architecture of NP-PCNF provides fast electron/ion transport pathways, while nitrogen and phosphorus co-doping enhances redox kinetics through chemisorption and catalytic conversion of polysulfides. As a result, RT Na-S batteries incorporating NP-PCNF exhibit a high specific capacity of 1147.7 mAh g-1 at 0.5 C, excellent rate capability (550 mAh g-1 at 2 C), and outstanding long-term cycling stability over 300 cycles with an ultra-low capacity decay rate of 0.04 % per cycle. This study provides valuable insights into the design of heteroatom-doped porous carbon nanofiber networks for high-performance, free-standing electrode membranes and offers an effective strategy for suppressing the shuttle effect in RT Na-S batteries.