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

Niobium boride (NbB₂) 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 NbB₂@boron-doped carbon (NbB₂@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 NbB₂ 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 NbB₂ but also accelerates the transfer of polysulfides and electron diffusion across the heterogeneous interface and consequently maintains moderate sulfur adsorption-desorption dynamics. The resulting NbB₂@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.