Tailoring Coordination Micro-Environments in Metal-Based Molecular Complexes to Homogeneously Catalyze Li─S Battery Reactions

The performance of lithium-sulfur (Li─S) batteries is severely constrained by fatal polysulfide shuttling, sluggish sulfur redox kinetics, and uncontrollable lithium deposition. Organic metal-based molecules have recently emerged as a novel type of promoters capable of modulating sulfur and lithium species evolution through either heterogeneous or homogeneous mechanisms to respond these issues. Herein, homogeneous metal-based phenanthroline molecular catalysts are developed by tailoring coordination micro-environments within electrolyte. By altering metal center type, the Co-based complex in the electrolyte (Co-ETL) shows an identical coordination geometry of Co–N₄, whereas the Fe-based complex in the electrolyte (Fe-ETL) exhibits dual Fe─N₂/Fe─N₄ coordination structures. Specifically, the Fe─N₂ coordination enhances adsorption of sulfur and lithium species, whereas the Fe─N₄ coordination promotes lithium atom diffusion more efficiently. Such a rational functionality division remarkably enhance the homogeneous optimization activity of the Fe-ETL toward the kinetically favorable sulfur cathode reactions and improved lithium anode stability. Therefore, the battery demonstrates stable cycling at 5.0 C over 500 cycles with a low degradation of 0.03% per cycle. Even under a sulfur loading of 7.1 mg cm⁻², the battery delivers a remarkable initial areal capacity of 6.4 mA h cm⁻² and maintains a favorable cycling stability.