Metal–organic framework derived Fe7S8 nanoparticles embedded in heteroatom-doped carbon with Lithium and Sodium storage capability

Iron sulfides are promising materials for lithium- and sodium-ion batteries owing to their high theoretical capacity and widespread abundance. Herein, the performance of an iron sulfide-carbon composite, synthesized from a Fe-based metal–organic framework (Fe-MIL-88NH2) is reported. The material is composed of ultrafine Fe7S8 nanoparticles (<10 nm in diameter) embedded in a heteroatom (N, S, and O)-doped carbonaceous framework (Fe7S8@HD-C), and is obtained via a simple and efficient one-step sulfidation process. The Fe7S8@HD-C composite, investigated in diethylene glycol dimethyl ether-based electrolytes as anode material for lithium and sodium batteries, shows high reversible capacities (930 mAh g−1 for lithium and 675 mAh g−1 for sodium at 0.1 A g−1). In situ X-ray diffraction reveals an insertion reaction to occur in the first lithiation and sodiation steps, followed by conversion reactions. The composite electrodes show rather promising long-term cycling stability and rate capability for sodium storage in glyme electrolyte, while an improved rate capacity and long-term cycling stability (800 mAh g−1 after 300 cycles at 1 A g−1) for lithium can be achieved using conventional carbonates.