Fe–Se–Ni Synergistic Nanoreactors in Hierarchical Porous Fe ₂ NiSe ₄ @rGO Hosts for High-Rate Lithium–Sulfur Batteries

The rational design of efficient electrocatalysts is critical for overcoming the polysulfide shuttle and sluggish kinetics in lithium-sulfur (Li-S) batteries. Herein, we developed a hierarchically porous Fe₂NiSe₄/reduced graphene oxide (FNS@rGO) composite as an advanced sulfur host. This architecture leverages synergistic Fe³⁺/Ni²⁺ d-orbital hybridization to optimize polysulfide adsorption and conversion energetics. Fe centers enhance chemisorption through polarized Fe-Se bonding, while Ni sites facilitate rapid sulfur redox mediation via accessible Ni²⁺/Ni³⁺ transitions. The integrated rGO matrix ensures dual functionality: enabling efficient charge transport and confining polysulfide diffusion. The FNS@rGO electrodes exhibit outstanding rate capability (546 mAh g^-1 at 4 C), remarkable cycling stability (0.041% capacity decay per cycle over 500 cycles at 1 C, 0.047% capacity decay per cycle over 300 cycles at 4 C), and 7.4 mAh cm^-2 areal capacity under high sulfur loading (8.1 mg cm^-2). Practical viability is confirmed by stable pouch cell operation for over 80 cycles. Mechanistic studies provide critical insights, including in situ Raman and XPS analysis, which verify that Fe sites enhance polysulfide chemisorption via polarized Fe-Se bonding, while adjacent Ni sites accelerate bidirectional sulfur redox through facile Ni²⁺/Ni³⁺ transitions. This work establishes key design principles for bimetallic chalcogenides in high-energy storage systems.