ZnFe2O4 hollow rods enabling accelerated polysulfide conversion for advanced lithium-sulfur batteries

The high energy density and favorable cost-effectiveness make lithium-sulfur (Li-S) batteries one of the most attractive energy storage systems. However, the low sulfur utilization and poor cycle life, resulting from the losses of soluble polysulfide intermediates, and their sluggish redox conversion process, severely impede practical applications of reliable Li-S batteries. Effectively inhibiting the polysulfide diffusion and accelerating their conversion is beneficial to enhance the performance of sulfur cathodes. Herein, a novel carbon-free ZnFe2O4 hollow rod has been developed as an advanced host material to confine polysulfides within the cathode and accelerate the redox conversion during cycling. The soluble polysulfides anchored by the ZnFe2O4 hollow rod structure are shown to be rapidly converted to sulfur and lithium sulfides. Detrimental polysulfide diffusion is therefore effectively inhibited. The redox kinetics of sulfur cathodes has been systematically investigated, revealing that the ZnFe2O4 host can improve the activity for Li2S deposition, facilitate lithium-ion diffusion, and lower the reaction energy barriers for the multistep phase transition of sulfur. As a result, the developed S@ZnFe2O4 composite cathodes exhibit an improved cycling capacity of 1158 mAh g-1. These results demonstrate that the accelerated redox conversion of anchored polysulfides is essential for enhancing the electrochemical performance of Li-S batteries.