Simultaneously tuning the defect and morphology to design urchin-like Fe-Co₃O_4-x as integrated trapping-catalyzing modified separator for superior lithium-sulfur batteries

The lithium-sulfur (Li-S) battery is a promising candidate for next-generation energy storage devices because of its high energy density and cost-effectiveness. However, its commercial application is still hampered by the severe lithium polysulfides (LiPSs) shuttling and the sluggish polysulfide redox kinetics. Herein, the defect-rich Fe-Co3O4-x with a unique 3D urchin-like architecture has been rationally designed using a microwave-assisted hydrothermal method followed by calcination. The morphology and surface defect of Fe-Co3O4-x are simultaneously regulated by altering the Fe doping content. The resulting Fe-Co3O4-x materials are confirmed with abundant oxygen defects and exhibit strong chemical entrapment towards LiPSs, as evidenced by both the experimental results and the DFT calculations. Under dual regulation, the nanorod-assembled urchin-like architecture could accelerate the electron/ion transport and significantly strengthen the LiPSs redox reaction kinetics. As expected, the assembled Li-S cell with Fe-Co3O4-x modified separator exhibits an ultralow capacity decay of 0.04% per cycle at 1 C after 800 cycles and excellent rate capability as high as 528 mAh g-1 at 5 C. Furthermore, the modification of Fe-Co3O4-x on the separator also improves the reversibility of the lithium anode deposition/stripping. This work provides new insights into effective strategies for designing 3D nanostructural oxygen defect-rich electrocatalysts to achieve advanced Li-S batteries.