Synergistic modification mechanism of Mn-doped and N-doped carbon-coated FeS composites and their application in lithium-ion batteries

Transition metal sulfides such as FeS are promising anode materials for lithium-ion batteries (LIBs) due to their high theoretical capacity and natural abundance. However, their practical application is hindered by poor electronic conductivity, severe volume expansion, and irreversible structural degradation. To overcome these limitations, we report a dual-regulation strategy that integrates Mn doping and nitrogen-doped carbon (NC) coating to synergistically enhance both the lattice structure and interface characteristics of FeS. The resulting Mn-FeS/NC composite exhibits anisotropic lattice expansion, with the (102) crystal plane spacing increasing from 0.209 nm to 0.263 nm. Density functional theory (DFT) calculations reveal that Mn doping significantly lowers the Li + insertion/extraction energy barrier. Meanwhile, the NC coating forms a highly conductive and flexible network that buffers volume changes and enhances interfacial stability. Benefiting from this multiscale synergy, Mn-FeS/NC delivers a high initial discharge capacity of 1660.4 mAh g −1 at 0.1 A g −1 with an initial Coulombic efficiency of 75.8 %, and maintains 728.9 mAh g −1 after 600 cycles at 1.0 A g −1 . Even at 5.0 A g −1 , a capacity of 413.6 mAh g −1 is retained. Kinetic analysis confirms a dominant pseudocapacitive behaviour, contributing up to 72.3 % at high scan rates. This study not only provides quantitative insight into the synergistic effect of Mn doping and NC encapsulation, but also offers a viable design strategy for high-performance metal sulfide anodes in next-generation LIBs.