Uniform Al2O3 coating for improved cycling stability of O3-type sodium-ion batteries cathode: Mechanisms and performance insights

Low-cost sodium-ion batteries have significant potential in large-scale energy storage applications owing to the abundant sodium reserves. Despite O3-type layered transition metal oxide cathode materials show the high energy density and initial coulombic efficiency, their structural instability and severe interface side reactions lead to a decline in cycling performance, posing notable challenges and obstacles to their large-scale commercialization. In this study, we propose a simple, direct, and practical strategy to coat the O3-NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode material surface with a protective Al 2 O 3 layer using Al(OH) 3 as the aluminum source. This method effectively suppresses the deleterious degradation of the bulk phases and surface during cycling, thereby improving the electrochemical performance of the material. It is proved that harmful decomposition of the electrolyte on the material's surface is reduced, and the interface stability is enhanced by characterization techniques such as XRD , SEM-EDS, TEM, and XPS . Stress and strain induced by sodium ion insertion and extraction, which cause particle fracture , are effectively alleviated by the rigid coating, improving the structural degradation in the near-surface region. The material with 0.5 wt% coating exhibits a capacity retention of 60.7 % (18.4 % higher than the uncoated sample) after 200 cycles at 1C rate and shows a lower interfacial transfer impedance. It is guided for optimizing the cycling stability of layered oxide cathode materials to the development of sodium ion battery technologies.