Ultrafast and Ultrastable Heteroarchitectured Porous Nanocube Anode Composed of CuS/FeS₂ Embedded in Nitrogen-Doped Carbon for Use in Sodium-Ion Batteries

The enhancement of the structural stability of conversion-based metal sulfides at high current densities remains a major challenge in realizing the practical application of sodium-ion batteries (SIBs). The instability of metal sulfides is caused by the large volume variation and sluggish reaction kinetics upon sodiation/desodiation. To overcome this, herein, a heterostructured nanocube anode composed of CuS/FeS₂ embedded in nitrogen-doped carbon (CuS/FeS₂@NC) is synthesized. Size- and shape-controlled porous carbon nanocubes containing metallic nanoparticles are synthesized by the two-step pyrolysis of a bimetallic Prussian blue analog (PBA) precursor. The simple sulfurization-induced formation of highly conductive CuS along with FeS₂ facilitates sodium-ion diffusion and enhances the redox reversibility upon cycling. The mesoporous carbon structure provides excellent electrolyte impregnation, efficient charge transport pathways, and good volume expansion buffering. The CuS/FeS₂@NC nanocube anode exhibits excellent sodium storage characteristics including high desodiation capacity (608 mAh g^–1 at 0.2 A g^–1), remarkable long-term cycle life (99.1% capacity retention after 300 cycles at 5 A g^–1), and good rate capability up to 5 A g^–1. The simple, facile synthetic route combined with the rational design of bimetallic PBA nanostructures can be widely utilized in the development of conversion-based metal sulfides and other high-capacity anode materials for high-performance SIBs.