Construction of Small FeS₂ Nanoparticles Embedded in Porous Nitrogen-Doped Carbon with Enhanced Sodium Ion Storage Properties

Iron disulfide (FeS₂) is a potentially suitable anode material for sodium-ion batteries (SIBs) by virtue of its high theoretical capacity (894 mAh g⁻¹). Unfortunately, the inferior electrical conductivity, sluggish diffusion kinetics, and large volume changes have impeded its practical application. Here, we report a composite material comprising numerous small FeS₂ nanoparticles intimately embedded in a porous N-doped carbon framework through high-energy ball milling combined with stepwise post-thermal treatment. The highly porous and robust external carbon framework serves as a conductive substrate and has good strain accommodation for small FeS₂ nanoparticles, which can not only boost electron/ion transport ability of the composite but also provide extra active sites for sodium ion storage and maintain the structural integrity of the composite during repeated cycling processes. As a result, the FeS₂/PNC electrode achieves high initial Coulombic efficiency of 81%, reversible specific capacities of 530 mA h g⁻¹ with good capacity retentions of 95% after 200 cycles at 1 A g⁻¹ , and a superior rate capability (376 mA h g⁻¹ at 5 A g⁻¹). The promising electrochemical performance and the facile synthesis method make the FeS₂/PNC composite a potential candidate material as a SIBs anode for large-scale preparation and application in the future.