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.