Regulating the interfacial electric field of NbP-NbC heterostructures to efficiently inhibit polysulfide shuttling in Li-S batteries

The commercial application of lithium-sulfur batteries is severely hampered by polysulfide shuttle effects. We predicted a novel niobium phosphide-niobium carbide heterostructure as a productive polysulfide adsorbent and catalytic material for Li-S batteries and successfully synthesized a NbP-NbC heterostructure, which was evenly dispersed on porous carbon (NbP-NbC/C). Density functional theory calculations indicated that the heterostructure between NbP and NbC regulated the interfacial electric field, promoting electron transfer and decreasing the reaction energy barrier to accelerate the transformation of polysulfides. The heterostructure induced interfacial charge redistribution, transferring more electrons to the surface and facilitating rapid lithium-ion transport while accelerating polysulfide transfer. This provided moderate polysulfide absorbability and further enhanced the intrinsic catalytic activity of NbP-NbC/C. Furthermore, in situ characterization and catalytic experiments were conducted to verify that the NbP-NbC/C heterostructure exhibited excellent cycling stability and electrochemical and catalytic properties. Accordingly, the NbP-NbC/C@S cathode showed a high reversible capacity (1367.9 mA h g-1 at 0.2C) and stable long-life span with 250 cycles (approximate to 89% retention at 0.2C). Importantly, the thick sulfur cathode (sulfur loading: 8.2 mg cm-2) presented a large area capacity of 6.5 mA h cm-2, and the NbP-NbC@S||Li flexible Li-S pouch cell demonstrated an excellent initial energy density value of 451 W h kg-1. A novel NbP-NbC heterostructure with interfacial electric field provides moderate polysulfide absorbability and further enhances the intrinsic catalytic activity for Li-S batteries.