NiFeP Anchored on rGO as a Multifunctional Interlayer To Promote the Redox Kinetics for Li–S Batteries via Regulating d-Bands of Ni-Based Phosphides

Sluggish kinetics of polysulfide redox reaction give rise to poor electrochemical properties for lithium–sulfur (Li–S) batteries. Electrocatalysts are introduced to decrease activation energy and effectively accelerate the dynamics of polysulfide conversion. In this study, we propose a rational strategy of tuning the d-band of catalysts via delivering Fe into Ni2P in situ grown on rGO to construct NiFeP/rGO composites. Based on the first-principles density functional theory calculation, the metallic conduction of Ni2P could be improved by Fe incorporation, facilitating a charge transfer electrocatalytic interface for redox reaction of LiPSs. Moreover, the d-band center of NiFeP also elevates to the Fermi level after incorporation with Fe, which could weaken the S–S bonds of polysulfides due to its redistributed electron population and reduce the activation barrier. Therefore, NiFeP/rGO composites as the functional interlayer for Li–S batteries can not only promote the interaction between polysulfides and NiFeP but also accelerate the conversion of polysulfides. They exhibit a high initial discharge capacity of 1261 mAh g–1 at 0.2 C and an outstanding rate reversible capacity of 671 mAh g–1 even at a high rate of 2 C. The high-efficiency NiFeP/rGO electrocatalyst with a rational structure for Li–S batteries testifies to the availability of the d-band regulating strategy with the low-activation-energy barrier and promotes an in-depth understanding of LiPSs redox reaction at the molecular or atom level.