Regulating the d-p band center of FeP/Fe2P heterostructure host with built-in electric field enabled efficient bidirectional electrocatalyst toward advanced lithium-sulfur batteries.

• A favorable preparation strategy toward FeP/Fe 2 P heterostructure is proposed by regulating the calcination temperature of phosphating process. • Deciphering the role of energy gap between cation 3d and anion 2p band in regulating the adsorption and catalysis of polysulfides. • The charge migration and an internal electric field of FeP and Fe 2 P are induced after reaching a thermodynamic equilibrium state. Exploring advanced electrocatalysts and understanding their mechanism in regulating polysulfides-transformation is of great importance but a challenging task for lithium-sulfur batteries (LSBs). Herein, FeP/Fe 2 P heterostructure nanoparticles with an internal electric field, prepared by a temperature-controlled phosphating process, can effectively improve the electrocatalytic activities of the bidirectional Li 2 S deposition/dissolution. This improvement can be attributed to the modulating absorptivity of lithium polysulfides (LiPSs) and propelling charge transfer. The reduced d-p band center between bonding and antibonding orbitals of the Fe 3d and P 2p band in the heterostructure enables bonding with LiPSs to achieve a higher electronic concentration at the Fermi level. This regulates the adsorption-diffusion-conversion process, reduces the activation energy, and improves the Li+ diffusion. Benefiting from the boosted kinetics of the FeP/Fe 2 P heterostructure, the cells exhibit a high reversible capacity of 1412 mAh g−1 at 0.1 C and outstanding energy efficiency of ∼ 90% from 0.1 C to 2 C. Furthermore, the cell with high sulfur loading of 4 mg cm−2 demonstrates a high capacity of 786 mAh g−1 after 100 cycles at 0.5 C. This work presents an effective method and favorable guidance for developing advanced heterostructures in LSBs. [ABSTRACT FROM AUTHOR]