Dual Carbon Modification and Pore Structure Regulation of CuS/FeS₂ Bimetallic Sulfides via Multifunctional Additives toward High-Rate and Durable Sodium Storage

FeS₂ has garnered extensive attention as a potential anode material for sodium-ion batteries because of its cost-effectiveness, abundance, and high theoretical capacity. Nonetheless, the utilization of FeS₂ faces challenges arising from its sluggish reaction kinetics and insufficient structural stability, causing significant volume changes and rapid capacity degradation during cycling. To tackle these challenges, we propose a strategy involving dual carbon modification and regulation of pore structure to create heterogeneous CuS/FeS₂ particles embedded in N-doped porous carbon matrix (CuS/FeS₂/NPC-MP). This composite is synthesized from CuFe-PBA precursor via sequential ball milling, carbonization, and sulfurization processes. The introduction of melamine and polyethylene glycol as additives facilitates the creation of interconnected NPC, which possesses robust structural integrity and abundant mesopores, increasing the specific surface area, promoting efficient electron/ion transport, and mitigating volume fluctuations. Furthermore, the formation of CuS/FeS₂ heterostructures enhances the capacity and diffusion kinetics through the internal electric field. The CuS/FeS₂/NPC-MP anode achieves a high capacity (681 mA h g^-1 at 1 A g^-1), exceptional rate capability (572 mA h g^-1 at 5 A g^-1), and excellent long-term cycling stability (90.5% retention after 2000 cycles at 5 A g^-1). This work provides new design paradigms for developing high-performance metal sulfide anodes toward fast charging and long-lasting sodium storage.