Engineering Fe-N Coordination Structures for Fast Redox Conversion in Lithium-Sulfur Batteries.

Critical drawbacks, including sluggish redox kinetics and undesirable shuttling of polysulfides (Li2 Sn , n = 4-8), seriously deteriorate the electrochemical performance of high-energy-density lithium-sulfur (Li-S) batteries. Herein, these challenges are addressed by constructing an integrated catalyst with dual active sites, where single-atom (SA)-Fe and polar Fe2 N are co-embedded in nitrogen-doped graphene (SA-Fe/Fe2 N@NG). The SA-Fe, with plane-symmetric Fe-4N coordination, and Fe2 N, with triangular pyramidal Fe-3N coordination, in this well-designed configuration exhibit synergistic adsorption of polysulfides and catalytic selectivity for Li2 Sn lithiation and Li2 S delithiation, respectively. These characteristics endow the SA-Fe/Fe2 N@NG-modified separator with an optimal polysulfides confinement-catalysis ability, thus accelerating the bidirectional liquid-solid conversion (Li2 Sn ↔Li2 S) and suppressing the shuttle effect. Consequently, a Li-S battery based on the SA-Fe/Fe2 N@NG separator achieves a high capacity retention of 84.1% over 500 cycles at 1 C (pure S cathode, S content: 70 wt%) and a high areal capacity of 5.02 mAh cm-2 at 0.1 C (SA-Fe/Fe2 N@NG-supported S cathode, S loading = 5 mg cm-2 ). It is expected that the outcomes of the present study will facilitate the design of high-efficiency catalysts for long-lasting Li-S batteries.