Hierarchical porous carbon nanofibers embedded with ultrafine Nb2O5 nanocrystals for polysulfide-trapping-conversion Li-S batteries

The practical application of lithium-sulfur (Li-S) batteries is severely impeded by the sluggish redox kinetics and polysulfides shuttling. Herein, hierarchical porous carbon nanofibers (HPCNF) embedded with ultrafine Nb2O5 nanocrystals (denoted as Nb2O5-HPCNF) are designed and served as a duplex-functional separator for polysulfide trapping and kinetic enhanced Li-S batteries. The hierarchical porous structure serves as a reservoir for polysulfide trapping, and HPCNF network provides channels for fast electron/ion transport. More importantly, the built-in Nb2O5 nanocrystals enhance the chemical affinity of polysulfides, and simultaneously promote the liquid-solid conversions of polysulfides. As a result, the Li-S batteries with Nb2O5-HPCNF separator delivered a high initial capacity of 1393 mAh g-1 at 0.2 C and a high capacity of 741 mAh g-1 even at 4.0 C. Moreover, the modified cell can remain 574 mAh g-1 after 600 cycles at 1.0 C, corresponding to an ultralow decay rate of 0.066% per cycle. This work provides a rational design for achieving high-performance Li-S batteries.