Rapid mechanochemical synthesis of high-performance NaFeAl(PO)(PO)/C cathode material for sodium-ion storage.

NaFe(PO)(PO) is regarded as a promising cathode material for sodium-ion batteries due to its affordability, non-toxic nature, and excellent structural stability. However, its electrochemical performance is hampered by its poor electronic conductivity. Meanwhile, most of the previous studies utilized spray-drying and sol-gel methods to synthesize NaFe(PO)(PO), and the large-scale synthesis of the cathode material is still challenging. This study presents a composite cathode material, NaFeAl(PO)(PO)/C, prepared via a straightforward ball-milling technique. By substituting Al minimally into the Fe site of NFPP, Fe defects are introduced into the structure, hindering the formation of NaFePO and thereby enhancing Na-ion diffusion kinetics and conductivity. Additionally, the average length of AlO bonds (2.18 Å) is slightly smaller than that of FeO bonds (2.19 Å), contributing to the superior structural stability. The smaller ionic radii of Al induce lattice contraction, further enhancing the structural stability. Moreover, the surface of material particles is coated with a thin layer of carbon, ensuring excellent electrical conductivity and outstanding structure stability. As a result, the NaFeAl(PO)(PO)/C cathode exhibits excellent electrochemical performance, leading to high discharge capacity (128.1 mAh g at 0.2 C), outstanding rate performance (98.1 mAh g at 10 C), and long cycle stability (83.7 % capacity retention after 3000 cycles at 10 C). This study demonstrates a low-cost, ultra-stable, and high-rate cathode material prepared by simple mechanical activation for sodium-ion batteries which has application prospects for large-scale production.