Co-NC/Nb2O5 heterostructure enable the synergistic fast sulfur redox kinetics and uniform lithium deposition for advanced lithium sulfur batteries

Abstract

Lithium‑sulfur batteries (LSBs) have attracted much attention due to their high theoretical energy density (2600 Wh kg^-1) and low cost of sulfur cathodes. However, their practical application is hindered by the significant polysulfide shuttle effect and sluggish redox kinetics. To address these challenges, a Co-NC/Nb₂O₅ heterostructure was successfully prepared through high-temperature annealing of a ZIF-67 precursor followed by hydrothermal growth of Nb₂O₅ nanocrystals on the surface of Co-embedded and N-doped carbon polyhedrons (Co-NC). The unique structure features a hierarchical conductive framework with uniformly dispersed Nb₂O₅ nanoparticles and defect-rich carbon matrix, which synergistically enhances sulfur utilization and ion diffusion. Numerous dangling bonds and defective sites exist on the Nb₂O₅ surfaces, and its Lewis acidic site (Nb⁵⁺) can inhibit the solvation and shuttling of LiPSs through strong chemical interactions with the S atoms of polysulfides via Nb-O-S bonds. The catalytic and adsorption mechanisms were explained by density functional theory (DFT) calculations and experimental results. Consequently, LSBs cells equipped with Co-NC/Nb₂O₅ modified separators demonstrated exceptional electrochemical performance with a rate capability that provides a reversible capacity of 761.8 mAh g^-1 at 3 °C. The composite of MOF-derived hollow carbon polyhedra decorated with Nb₂O₅ nanoparticles ensured fast electron transfer, achieving a reversible capacity of 731.4 mAh g^-1 after 500 cycles at 1C and 501.6 mAh g^-1 after 1000 long cycles at 2C, with a capacity decay rate of only 0.03 % per cycle. Excellent electrochemical performance was maintained with a high sulfur loading cycling performance of 5 mg cm^-2 at a low electrolyte/sulfur condition of 7 μL mg^-1. This work provides new insights into the development of high energy density LSBs and the advancement of next generation energy storage systems through precise electronic structure design at the heterojunction interface.

Keywords: Chemisorption and catalytic conversion; Co-NC/Nb(2)O(5) heterostructure; Lithium‑sulfur batteries; Separator modification; Shuttle effect.