Nitrogen-Doped Porous Carbon Networks with Active Fe–Nx Sites to Enhance Catalytic Conversion of Polysulfides in Lithium–Sulfur Batteries

The practical development of lithium-sulfur (Li-S) batteries is largely obstructed by their poor cycling stability due to the shuttling effect of soluble polysulfides. To address this issue, we herein report an interconnected porous N-doped carbon network (NPCN) incorporating Fe3C nanoparticles and Fe-Nx moieties, which is used for separator modification. The NPCN can facilitate lithium ion and electron transport and localize polysulfides within the separator's cathode side due to strong chemisorption; the Fe3C/Fe-Nx species also provides chemical adsorption to trap polysulfides and Fe3C catalyzes the redox conversion of polysulfides. More importantly, the catalysis effect of Fe3C is promoted by the presence of Fe-Nx coordination sites as indicated by the enhanced redox current in cyclic voltammetry. Due to the above synergistic effects, the battery with the Fe3C/Fe-Nx@NPCN modified separator exhibits high capacity and good cycling performance: at a current density of 0.1C, it yields a high capacity of 1517 mAh g-1 with 1.2 mg cm-2 sulfur loading and only experiences a capacity decay rate of 0.034% per cycle after 500 cycles at 1C; it also delivers a good capacity of 683 mAh g-1 at 0.1C with a high sulfur loading of 5.0 mg cm-2; after 200 cycles, the battery capacity can still reach 596 mAh g-1, corresponding to 87% capacity retention. Our work provides a new and effective strategy to achieve the catalytic conversion of polysulfide and is beneficial for the development of rechargeable Li-S batteries.