Enhanced Cycling Stability and Rate Capability of Al₂O₃-Coated NaNi_1/3Fe_1/3Mn1_/3O₂ Cathodes for Sodium-Ion Batteries

Layered transition metal oxide cathode materials for sodium-ion batteries have garnered extensive attention for their high theoretical capacity and high initial coulombic efficiency. However, the surface stability of these materials still requires further improvement. In this paper, the effects of different Al₂O₃ coating levels on the properties of NaNi_1/3Fe_1/3Mn_1/3O₂ (NMF) were investigated. An innovative method is proposed to address the problems of dry coating nanomaterial particles that are easily agglomerated and difficult to be dispersed homogeneously, as well as the high cost of wet coating. We dispersed Al₂O₃ in a small amount of ethanol and added an appropriate amount of PVP as a dispersant to form a suspension, which was added to the high-speed rotating NMF reference material powder by spraying, and then heated at high temperature to obtain uniformly coated cathode materials. Our findings reveal that NMF cathodes coated with 0.3 wt.% Al₂O₃ and subjected to thermal treatment at 900°C exhibit higher initial discharge capacity of approximately 145 mAh/g at 0.1C in 2–4 V, with a sustained discharge capacity of nearly 120 mAh/g even at 5C. After 100 cycles at 1C, the capacity remained at 110 mAh/g, representing capacity retention of about 81%.