Adsorption-regulated carbon network construction in Na8Fe5(SO4)9 cathode for enhanced sodium storage kinetics

Sodium-ion batteries (SIBs) are promising alternatives to lithium-ion systems due to abundant resources and good low-temperature performance. However, iron-based sulfate cathodes suffer from poor electronic conductivity and unstable electrode–electrolyte interfaces. To address this, we combined DFT-guided interface design with a scalable synthesis method to build an optimized conductive network. Density functional theory (DFT) calculations identified the interfacial characteristics of weak sodium dodecyl sulfonate (SDS) adsorption and strong carbon adsorption, providing theoretical guidance for achieving uniform carbon dispersion and coating. Using sand-milling and spray-drying, we fabricated a Ketjenblack (KB)-coated core–shell cathode (NFS@KB-4%). The high-surface-area carbon enabled a continuous conductive network and self-assembly of primary particles into uniform spherical secondary particles (5–7.8 μm). This structure simultaneously enhanced electronic conductivity and structural stability. The NFS@KB-4% cathode delivered 84.03 mAh g−1 at 1 C, retained 91.1% capacity after 200 cycles, and exhibited a Na+ diffusion coefficient of 8.24 × 10−8 cm2 s−1—twice that of the control. A soft-pack full cell with hard-carbon anode maintained 97.2% capacity over 60 cycles, demonstrating practical viability. This work paves the way for large-scale use of high-rate, long-life iron-based sulfate cathodes in SIBs.