A "Catalysis-Immobilization-Deposition" Stepwise Strategy toward Dynamic Equilibrium of Polysulfides Conversion and Diffusion in Lithium-Sulfur Batteries.

Stepwise electrocatalysis can remarkably accelerate the kinetics of two consecutive reactions in sulfur electrochemistry. However, the significant difference between the catalysis and diffusion rates of polysulfides results in persistent shuttling in the stepwise electrocatalysts. Here, a stepwise electrocatalytic strategy of catalysis-immobilization-deposition is proposed for achieving the consistency of diffusion and catalysis of polysulfides. Accordingly, a sandwich-like stepwise electrocatalyst is designed, which is composed of Co nanoparticles (Co-NP), mesoporous SiO 2 , and iron single atom (Fe-SA) (denoted as Co-NP@SiO 2 @Fe-SA), serving as catalysis core, immobilization interlayer, and deposition shell, respectively. Benefitting from the dynamic equilibrium between production and consumption of polysulfides achieved by the spatial synergistic effect of the triple sites, the S/Co-NP@SiO 2 @Fe-SA cathode delivers a high reversible capacity of 731 mAh g -1 over 500 cycles at 1 C with a small capacity decay of 0.039% per cycle. Moreover, a high areal capacity of 3.8 mAh cm -2 at a sulfur loading of 4.5 mg cm -2 is achieved with a low electrolyte/sulfur ratio of 5.9. This work sheds light on a new host design concept with high catalytic activity, stability, and selectivity to enable high performance lithium-sulfur batteries.