Ultrathin Nanosheets of Iron Nitride–Iron Oxide Heterostructures as Amphiphilic Separator Modification Layer for Lithium–Sulfur Batteries

The shuttling and sluggish dynamics of lithium polysulfides (LiPSs), as well as the uncontrollable Li dendrites, are the main difficulties hindering the further development of lithium–sulfur (Li–S) batteries. Herein, amphiphilic FexN–Fe2O3 heterostructures for amphiphilic modification of Li–S separators were prepared. It simultaneously alleviated the above issues from both the sulfur cathode and Li anode aspects. On the one hand, the heterostructure catalyst retained the excellent LiPS adsorption property of iron oxide while obtaining the good electronic conductivity of iron nitride. Combining the positive promoting effect of heterointerfaces on charge transfer, it efficiently completed the “adsorption-migration-conversion” process of sulfur species, not only alleviating the dissolution of LiPSs but also enhancing the electrode kinetics. On the other hand, the lithiophilic iron nitride and uniform two-dimensional porous structure promoted the homogenization of Li–ion flux, significantly reducing the degree of dendrite formation at the Li deposition surface. After coupling these functions, the FexN–Fe2O3-based Li–S cell achieved enhanced electrochemical performance, including an outstanding rate capacity of 465 mAh g–1 at 4 C, and cycling stability under a high area capacity of 4 mAh cm–2.