B–Nb–C Bond-Mediated Heterogeneous Interface Passivation for Enhanced Li–S Battery Performance

Niobium boride (NbB 2 ) shows an attractive catalysis performance for accelerating polysulfide conversion yet is challenging in lithium–sulfur batteries. Its excessively strong affinity toward sulfur species, particularly at Nb-terminated sites, results in irreversible surface passivation and eventually leads to catalyst poisoning. Although conventional heterogeneous coatings can mitigate the aforementioned issue, they suffer from weak physical interfacial contact with a marked increase in interfacial resistance. Herein, we constructed NbB 2 @boron-doped carbon (NbB 2 @BC) nanowires with B–Nb–C bond-mediated heterogeneous interface passivation for separator modification. Experiments and DFT theoretical calculations reveal that a spontaneous built-in electric field (BIEF) is formed between NbB 2 and BC, promoting the redistribution of interfacial charges. The B–Nb–C chemical bonds serve as a conductive “bridge” connecting the heterogeneous interface, pumping more electrons to the BC surface, which not only weakens the strong adsorption capacity of NbB 2 but also accelerates the transfer of polysulfides and electron diffusion across the heterogeneous interface and consequently maintains moderate sulfur adsorption–desorption dynamics. The resulting NbB 2 @BC/PP exhibits an excellent performance. Under a high sulfur loading (4.03 mg cm –2 ) and a low E/S (12 μL mg –1 ), a high capacity of 912.7 mAh g –1 and 87% retention after 50 cycles are achieved. This work provides an innovative interface engineering strategy for developing electrocatalysts that are resilient to poisoning.