Boosting bidirectional sulfur conversion enabled by introducing boron-doped atoms and phosphorus vacancies in Ni2P for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have gained great attention due to the high theoretical energy density and low cost, yet their further commercialization has been obstructed by the notorious shuttle effect and sluggish redox dynamics. Herein, we supply a strategy to optimize the electron structure of Ni₂P by concurrently introducing B-doped atoms and P vacancies in Ni₂P (V_p-B-Ni₂P), thereby enhancing the bidirectional sulfur conversion. The study indicates that the simultaneous introduction of B-doped atoms and P vacancies in Ni₂P causes the redistribution of electron around Ni atoms, bringing about the upward shift of d-band center of Ni atoms and effective d-p orbital hybridization between Ni atoms and sulfur species, thus strengthening the chemical anchoring for lithium polysulfides (LiPSs) as well as expediting the bidirectional conversion kinetics of sulfur species. Meanwhile, theoretical calculations reveal that the incorporation of B-doped atoms and P vacancies in Ni₂P selectively promotes Li₂S dissolution and nucleation processes. Thus, the Li-S batteries with V_p-B-Ni₂P-separators present outstanding rate ability of 777 mA h g⁻¹ at 5 C and high areal capacity of 8.03 mA h cm⁻² under E/S of 5 μL mg⁻¹ and sulfur loading of 7.20 mg cm⁻². This work elucidates that introducing heteroatom and vacancy in metal phosphide collaboratively regulates the electron structure to accelerate bidirectional sulfur conversion.