Mechanism investigation of iron selenide as polysulfide mediator for long-life lithium-sulfur batteries

The notorious issues of polysulfide shuttling behaviour and sluggish redox kinetics seriously hamper the practical applications of lithium-sulfur (Li-S) batteries. In this work, catalytic FeSe2 nanoparticles encapsulated with carbon nanoboxes (FeSe2@C NBs) that derived from the selenide reaction of yolk-shelled Fe3O4@C are proposed as a multifunctional sulfur host to restrain the polysulfide shuttle effect and accelerate the polysulfide redox conversion. The experimental results display that the S/FeSe2@C cathode exhibits better sulfur utilization, higher rate performance, and longer cycle life compared to S/Fe3O4@C cathode. Even after 700 cycles at 1C, an ultralow capacity decay of 0.04% per cycle of S/FeSe2@C cathode can still be maintained. The density functional theory (DFT) calculations reveal that FeSe2@C NBs possess stronger chemical affinity to polysulfides and lower energy gap between bonding and antibonding orbitals, which could promote the interfacial charge transfer kinetics, thus enabling better Li-S battery performance.