Polysulfide Trapping and Conversion Catalyzed by Manganese–Iron Oxide Coordinated Graphitic Carbon Nitride for Lithium–Sulfur Battery

Lithium–sulfur (Li–S or LSBs) batteries are promising next-generation energy-storage systems due to their high theoretical energy density. However, their practical application is limited by the sluggish kinetics of sulfur redox reactions and the severe polysulfide shuttle effect. Here, the study of an amorphous bimetallic manganese–iron oxide coordinated within a C-substituted g-C3N4 matrix via a microwave-assisted drying process followed by annealing is presented, intended for use as a high-performance cathodic interlayer. The incorporation of Mn and Fe oxides into the g-C3N4 framework generates abundant active sites, enhances ion diffusion, and accelerates the catalytic conversion of lithium polysulfides. The optimized MnFe-CN-2 sample (Mn/Fe precursor ratio of 3:2) delivers a high initial specific capacity of ∼1293 mAh g–1 at 0.1C and achieves a ∼748 mAh g–1 at a high rate of 4C, along with a capacity retention of ∼65% after 1000 cycles at 4C. Comprehensive analyses, including electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), cyclic voltammetry (CV), and UV–vis spectroscopy, reveal that the enhanced performance arises from markedly reduced charge transfer and diffusion resistances. The amorphous Mn–Fe active sites effectively catalyze sulfur redox reactions while simultaneously suppressing the polysulfide shuttle by strongly anchoring soluble intermediates. This work demonstrates a robust and scalable strategy for designing efficient interlayer materials to enable the practical realization of high-performance Li–S batteries.