Built-in electric field driving d-band center modulation and orbital hybridization in FeP/CoP heterojunctions to enable optimized polysulfide redox kinetics in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries face polysulfide shuttling and sluggish redox kinetics. Modulating adsorption strength is critical because a weak adsorption fails to adequately confine polysulfides (LiPSs), while strong adsorption passivates catalytic sites. As adsorption strength is governed by the d-band center (ε_d), regulating the electronic structure enables balanced LiPSs binding. Hence, a hollow tubular FeP/CoP heterojunction was constructed to regulate the interfacial electronic structure. As demonstrated, the built-in electric field established at the heterointerface drives spontaneous electron transfer from FeP to CoP, inducing interfacial charge redistribution. This electronic modulation shifts the ε_d value to an optimized value of −2.084 eV, achieving balanced σ* orbital filling for modulating LiPSs adsorption. Meanwhile, enhanced π* filling accelerates interfacial charge transfer and induces spin-state transitions that activate additional 3d states to promote d-p orbital hybridization with sulfur species, thus lowering Li₂S nucleation/decomposition barriers. Benefiting from this synergistic electronic modulation, the Li-S cells with FeP/CoP-modified separators deliver a high initial capacity of 1397.4 mAh/g at 0.2 C, excellent rate capability (671.4 mAh/g at 5.0 C), and stable long-term cycling. This work establishes that heterojunction-induced d-band engineering, coupled with orbital hybridization optimization and spin-state modulation, provides an effective strategy for synergistically regulating adsorption and catalysis in Li-S batteries.