Prussian Blue Analogue Derived CoS₂/FeS₂ Confined in N, S Dual-Doped Carbon Nanofibers for Sodium Storage

Pyrite iron disulfide (FeS₂) has aroused wide attention owing to its high theoretical capacity, making it a promising anode material for sodium-ion batteries (SIBs). Unfortunately, the poor electrical conductivity, large volume variation, and sluggish ion-migration kinetics lead to inferior rate capability and cycle stability, thus limiting its practical application. Herein, utilizing Prussian blue analogues (PBAs) as precursors, hollow heterostructured CoS₂/FeS₂ nanoparticles confined in N, S dual-doped carbon nanofibers (denoted as H-CoS₂/FeS₂@CNFs) are successfully developed via facile electrospinning, carbonization, and gas sulfurization processes. The effective combination of a unique hollow heterostructure and highly conductive N, S dual-doped CNFs can accelerate electron transport and ion diffusion kinetics, avoid aggregation of active materials, and obtain enhanced structural stability. As expected, the optimal H-CoS₂/FeS₂@CNFs-2 hybrid composite delivers a high reversible capacity of 542.6 mA h g^–1 after 150 cycles at 0.5 A g^–1 and outstanding cycling stability with a capacity of 323.7 mA h g^–1 over 1500 cycles at 5.0 A g^–1, showing the excellent sodium storage capability for SIBs. The rational design offers inspiration for fabricating high-performance bimetallic sulfides as anodes of SIBs through spatial confinement and a heterogeneous interface engineering strategy.