CoFe2O4@rGO as a Separator Coating for Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are hindered by the undesired shuttle effect and sluggish electrochemical conversion kinetics. Herein, a well-designed CoFe2O4@reduced graphene oxide (CFO@rGO) composite is used to modify the separator to develop a multifunctional polysulfide barrier. Density functional theory (DFT) calculations confirm that highly electronegative oxygen ions in CFO tend to bond with transition metal (TM) ions at octahedral (O-h) sites, which induces the formation of Fe-S and Co-S bonds between CFO and polysulfides. This indicates that CFO can effectively anchor polysulfides. Furthermore, the low Li2S decomposition energy barrier and Li+ diffusion energy barrier reveal that CFO can accelerate the redox reaction kinetics of sulfur species. Electronic structure calculations speculate that the low-energy barrier can be attributed to the electron-hopping phenomenon between TM ions of different valence states at O-h sites. Benefiting from these advantages, a CFO@rGO/PP separator demonstrates satisfactory cycling performance (0.087% capacity decay rate at 2C with 500 cycles) and superb rate performance (686 mAh g(-1) at 5C). This work provides a valuable reference for future research on spinel-type materials as electrocatalysts for Li-S batteries.