In situ synthesis of an ultrafine heterostructural Nb2O5–NbC polysulfide promotor for high-performance Li–S batteries

Abstract

Lithium–sulfur (Li–S) batteries are one of the most promising next-generation energy storage systems. Nevertheless, the notorious lithium polysulfide (LiPS) shuttle and sluggish sulfur redox kinetics result in inferior electrochemical performances, which are the major obstacles to their commercial application. Engineering the surface/interface of the ultrafine polysulfide promotor which can accelerate LiPS conversion and improve sulfur utilization is still challenging. Herein, we propose an effective strategy to synthesize ultrafine heterostructural Nb₂O₅–NbC homogeneously distributed in a carbon nanofiber matrix. Polystyrene (PS), as the nanocrystallite growth modulator, plays a vital role in suppressing particle agglomeration. The in situ formed heterostructures with a rational interface engineering design can achieve effective LiPS regulation and speed up the redox kinetics, as confirmed by the density functional theory (DFT) calculations and experimental characterizations. As expected, the battery containing ultrafine Nb₂O₅–NbC heterostructures delivers long-term cyclability with a low capacity decay of 0.044% per cycle over 800 cycles at 1.0C. And the decay rate is as low as 0.045% after 250 cycles at 0.5C with a sulfur loading of 4.0 mg cm⁻². This work provides a rational way to prepare ultrafine heterostructural polysulfide promotors via engineering the interface design for Li–S batteries.