A D‐Band Engineered Medium‐Entropy Metal Phosphide for Accelerated Lithium Polysulfide Conversion

ABSTRACT Lithium–sulfur (Li–S) batteries have emerged as a promising next‐generation energy storage technology owing to their high theoretical energy density. However, their practical use is limited by challenges such as the polysulfide shuttle and the slow conversion kinetics of lithium polysulfides (LiPSs). Medium‐entropy metal phosphides offer a strong solution to these issues because they provide good electrical conductivity, tunable properties, and multiple catalytically active sites for the sulfur redox reaction (SRR). In this work, a medium‐entropy phosphide, Fe 0.58 Co 0.98 Ni 0.44 P (FCNP–MEMP), was synthesized and used as an SRR catalyst to speed up LiPS conversion and suppress the shuttle effect. Density functional theory (DFT) calculations show that electronic hybridization among the three metal components in FCNP–MEMP raises the overall electronic state of the system. This strengthens LiPS adsorption and promotes the rate‐determining step of LiPS conversion. Electrochemical tests further confirm the strong LiPS conversion ability of FCNP–MEMP, especially by enabling rapid 3D nucleation of Li 2 S, which greatly improves reaction kinetics. As a result, Li–S cells with the FCNP–MEMP/C@S cathode show excellent cycling stability and rate performance. The corresponding pouch cell achieves a high initial energy density of 395.2 Wh kg − 1 , highlighting the practical potential of this catalyst design.