Optimizing O3-type cathode materials for sodium-ion batteries: Insights from precursor-based structural control and particle sizing strategies

Utilization of secondary spherical structures derived from metal hydroxides as precursor materials is one of the most promising approaches in terms of energy density and industrial viability for sodium-ion batteries. However, the understanding of how the particle size and arrangement of these secondary spherical structures influence electrochemical performance remains limited. Herein, a series of O3-type layered oxide cathode materials with various sizes (6, 8, 10, and 12 μm) and internal structures (hollow and radial arrangements) were tailored based on precursor-based structural control and particle sizing strategies. The relation in precursor size/structure, cathode characteristics, crystal microstress, structural stability, and electrochemical performance was established through a combination of structure, morphology, and electrochemical characterization. Notably, the size of secondary spherical particles exerted influence on microstress, leading to consequential changes in the c-axis. Elevated microstress levels induced compression of the unit cell along the c-axis, hampering sodium ion migration and undermining the stability of secondary spherical particles during cyclic charge-discharge processes. The optimized NaNi_1/3Fe_1/3Mn_1/3O₂-10 material exhibits the least micro stress and significant layer distance, delivers a capacity of 110 mAh g⁻¹, and maintains an impressive capacity retention rate of 91.8% after 100 cycles at 10 C. This work offers valuable insights in energy-density cathode materials in sodium ion batteries.