Architecting Freestanding Sulfur Cathodes for Superior Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have attracted extensive attention because of their low cost and high specific energy. RT Na-S batteries, however, usually suffer from sluggish reaction kinetics, low reversible capacity, and short lifespans. Herein, it is shown that chain-mail catalysts, consisting of porous nitrogen doped carbon nanofibers (PCNFs) encapsulating Co nanoparticles (Co@PCNFs), can activate sulfur via electron engineering. The chain-mail catalysts Co@PCNFs with a micrograde hierarchical structure as a freestanding sulfur cathode (Co@PCNFs/S) can provide space for high mass loading of sulfur and polysulfides. The electrons can rapidly transfer from chain-mail catalysts to sulfur and polysulfides during discharge-charge processes, therefore boosting its conversion kinetics. As a result, this freestanding Co@PCNFs/S cathode achieves a high sulfur loading of 2.1 +/- 0.2 mg cm(-2), delivering a high reversible capacity of 398 mA h g(-1) at 0.5 C (1 C = 1675 mA g(-1)) over 600 cycles and superior rate capability of an average capacity of 240 mA h g(-1) at 5 C. Experimental results, combined with density functional theory calculations, demonstrate that the Co@PCNFs/S can efficiently improve the conversion kinetics between the polysulfides and Na2S via transferring electrons from Co to them, thereby realizing efficient sulfur redox reactions.

Automated summary

In this study, it is demonstrated that a chain-mail catalyst Co@PCNFs can activate sulfur and improve the reaction kinetics in room-temperature sodium-sulfur batteries. The freestanding sulfur cathode constructed with Co@PCNFs achieves high reversible capacity and superior rate capability. This is attributed to efficient electron transfer between the polysulfides and Na2S enabled by the Co@PCNFs, enhancing sulfur redox reactions.