Binary Iron Sulfide as a Low-Cost and High-Performance Anode for Lithium-/Sodium-Ion Batteries

Iron-based sulfides have been deemed as an appealing anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) for their high theoretical capacity and low cost. However, their practical application is limited by drastic volume expansion during cycling and low-intrinsic electronic conductivity. In this work, we report a FeS₂/Fe₇S₈-rGO composite synthesized via a facile solvothermal method as an LIB/SIB anode. The FeS₂/Fe₇S₈-rGO anode exhibits an excellent Li-storage capacity of 514 mAh g^-1 at 2.0 A g^-1 after 3000 cycles and a Na-storage capacity of 650 mAh g^-1 at 0.2 A g^-1 after 250 cycles, respectively. The rGO matrix is deemed responsible for providing good electron conduction and alleviating volume expansion during cycling. The electrokinetic analysis confirms a large portion of intercalational pseudocapacitance as a major contribution to the superior rate performance. In situ X-ray diffraction further reveals details of a combined intercalational and conversional Li-ion storage mechanisms in this Fe-sulfide-based anode. Finally, density functional theory calculations suggest that there exists a synergistic effect at the heterointerface between FeS₂ and Fe₇S₈ to promote electrokinetics.