Integrating Ce doping and CeO2 coating for high stability of Ni/Mn-based layered oxide cathodes for sodium-ion batteries

P2-type layered oxides have emerged as leading cathode candidates in sodium-ion battery applications due to their superior ionic transport characteristics and competitive economic viability. However, the irreversible phase transitions during the charge/discharge process and severe interfacial parasitic reactions result in structural degradation and significant reduction in electrochemical performance, which poses a challenge for their largescale application. Herein, a dual-modification strategy involving Ce doping and CeO2 coating was developed via sol-gel synthesis to collaboratively improve the electrochemical performance of Na0.67Ni0.33Mn0.63Ce0.04O2 cathodes. The substitution of large radius of Ce4+ successfully expands the Na interlayer spacing, providing wider diffusion channels for Na+ extraction/insertion process. Simultaneously, the strong Ce-O bond enhances structural stability of the bulk phase, whereas the CeO2 coating mitigates electrolyte-induced corrosion. The modified cathode delivers a reversible capacity of 77.12 mA h g- 1 at a high rate of 30C, while maintaining of 76.5 % capacity retention after 1000 cycles at 1C. Therefore, co-modification of element doping and surface coating is an effective way to design cathode materials with excellent properties for sodium-ion batteries.