Favorable Moderate Adsorption of Polysulfide on FeNi₃ Intermetallic Compound Accelerating Conversion Kinetics for Advanced Lithium–Sulfur Batteries

Sluggish conversion kinetics of polysulfides during discharge and the severe shuttle effect significantly hinder the practical application of lithium-sulfur (Li-S) batteries. In this work, the lattice engineering strategy of Fe hybridization is employed to manipulate the bulk phase spacing of FeNi₃ (space group Pm3m) intermetallic compounds to adjust the 3d electronic structure, optimizing the adsorption of polysulfides, thereby accelerating the catalytic conversion. As a result, FeNi_2.25@OC achieves favorable moderate adsorption toward polysulfides. Due to the larger number of electrons occupying the lowest occupied molecular orbital of Li₂S₄, the S-S bonds are weakened and broken. Temperature-dependent experiments confirm that FeNi_2.25@OC exhibits the lowest activation energy and can effectively accelerate the catalytic conversion of polysulfides. The Li-S cell assembled with FeNi_2.25@OC modified PP separator delivers a high initial discharge specific capacity of 1219.5 mAh g^-1 at 0.2 C. Even at a high sulfur loading of 6.06 mg cm^-2 and lean electrolyte conditions (6 µL mg^-1), it can cycle stably for 60 cycles.