Contribution of different metal nodes on stepwise electrocatalysis in lithium-sulfur batteries

The mechanism of multifunctional sulfur-fixing materials on molecular / atomic level is important for selecting and designing effective electrocatalysts for lithium-sulfur batteries (LSBs). Therefore, metal coordination com-pounds (M = Co / Fe / CoFe) with unique catalytic behavior are selected as cathode additives to promote the sluggish reaction kinetics caused by multiphase conversion and focus on adsorption-catalysis mechanism. It is found that Co sites are conducive to promoting the generation of lithium sulfide that increase the specific discharge capacity, while Fe sites are beneficial for the adsorption of polysulfides that increase the capacity retention. The combination of Co and Fe sites can inhibit the polysulfides diffusion and induce the rapid and uniform deposition of lithium sulfide. Benefiting from the dual-anchoring of efficient Metal-S and Li-N bonds and special catalysis of Co sites, the CoFe PBA@S cells exhibit remarkable cyclability and capability. The cell delivers a small capacity fading rate (0.052% per cycle over 1000 cycles at 2 A g-1), excellent rate capability (811.86 mAh g-1 at 5 A g-1) and ultrahigh capability retention (1143.7 mAh g-1 after 100 cycles at 0.2 A g-1). Even with a high sulfur loading of 5 mg cm-2, it still shows reversible capacity of 789.7 mAh g-1 after 100 cycles at 0.2 A g-1. This work provides a rational direction to select and design effective electrocatalysts for LSBs.

Automated summary

The mechanism of multifunctional sulfur-fixing materials is crucial for the design of effective electrocatalysts for lithium-sulfur batteries (LSBs). Metal coordination compounds (M = Co / Fe / CoFe) are chosen as cathode additives to promote reaction kinetics and focus on adsorption-catalysis mechanism. The combination of Co and Fe sites inhibits polysulfides diffusion and induces rapid deposition of lithium sulfide, resulting in excellent cyclability and capacity retention for LSBs.