Spray‐Drying Synthesis of High‐Entropy‐Doped Na 2.5 Fe 1.75 (SO 4 ) 3 Cathodes With Enhanced Electrochemical Kinetics

ABSTRACT Alluaudite‐type Na 2+2x Fe 2− x (SO 4 ) 3 (NFS) has attracted considerable attention as a promising cathode for sodium‐ion batteries (SIBs), owing to its cost‐effective composition and relatively high operating voltage. Nevertheless, the further practical use of NFS is still hindered by its intrinsically low electronic conductivity, slow Na + transport kinetics, and insufficient stability of the cathode interface. Herein, a trace high‐entropy‐doped sodium iron sulfate cathode, Na 2.5 Fe 1.74125 (MgNiCuZnAl) 0.00175 (SO 4 ) 3 (HE‐NFS), is prepared by a spray‐drying method. Density functional theory (DFT) calculations show that high‐entropy doping narrows the electronic band gap and lowers the Na + diffusion energy barrier. As a result, HE‐NFS delivers a discharge capacity of 81.04 mAh g −1 even at 100 C. Analysis after cycling shows that a thin and uniform CEI layer was formed on HE‐NFS, which suppresses continuous electrolyte decomposition and interfacial side reactions. The capacity retention remains 83.1% after 500 cycles at 1 C. Moreover, HE‐NFS maintains stable electrochemical performance at −10°C and after air exposure, demonstrating its tolerance to low‐temperature operation and humid‐air storage. These results provide a resource‐efficient and scalable cathode‐manufacturing strategy for sustainable sodium‐ion energy storage toward carbon‐neutral energy systems.