Fe₇S₈/FeS₂ Heterostructures in Carbon Nanospheres for High-Performance Sodium Storage

Iron-based sulfides present significant potential as anode materials for sodium-ion batteries because of their remarkable theoretical capacity and outstanding electrochemical reversibility. However, challenges remain, including swift degradation of capacity resulting from a significant volumetric change and subpar rate performance attributed to slow electrochemical kinetics. Here, we employed a cost-effective and straightforward strategy to construct ultrasmall Fe7S8/FeS2 nanocrystals (∼22.8 nm) with a heterojunction structure encapsulated in cross-linked carbon nanospheres (Fe7S8/FeS2/CNs). The integration of ultrafine nanocrystals with a heterojunction architecture and an interconnected carbon sphere conductive framework enhances the structural stability and improves electrode reaction kinetics, effectively addressing the aforementioned challenges. Consequently, the synthesized Fe7S8/FeS2/CNs electrode demonstrates exceptional overall properties, characterized by high capacity (at 0.2 A/g delivers 741.6 mAh/g), outstanding rate performance (548.0 mAh/g at 5 A/g), and prolonged cycle life (at 2 A/g retains 472.1 mAh/g after 3000 cycles).