Spray-Drying Synthesis of High-Entropy-Doped Na2.5Fe1.75(SO4)3 Cathodes With Enhanced Electrochemical Kinetics

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.