Bulk-Interface Dual Strategy for Enhancing the Cycling Stability of P2-Type Layered Cathode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are attracting attention as cost-effective alternatives to lithium-ion batteries (LIBs) for large-scale energy storage. Among SIB cathodes, P2–Na 0.67 Ni 0.33 Mn 0.67 O 2 delivers high capacity and rate capability but suffers from rapid capacity fading under high-voltage charging due to a detrimental P2–O2 phase transition and interfacial side reactions. Here, we demonstrate a dual-modification strategy combining Cu 2+ doping and MgO surface coating to address these challenges. The dual-modified cathode (Na 0.67 Ni 0.28 Cu 0.05 Mn 0.67 O 2 @MgO) delivers markedly improved performance: a high-capacity retention of 90.88% after 200 cycles at 1 C and significantly enhanced rate capability (95.23 mAh g –1 at 10 C). Ex situ XRD analyses reveal that the P2–O2 phase transition is effectively suppressed, leading to minimal structural change during cycling. DFT calculations reveal that the Cu-MgO dual modification synergistically enhances the electronic conductivity of the electrode and suppresses transition-metal layer gliding. The results indicate that Cu 2+ doping enhances structural stability by regulating Na + /vacancy ordering and suppressing the high-voltage phase transition, whereas the MgO coating alleviates electrolyte-induced surface degradation and enhances Na + diffusion kinetics. This work offers a valuable reference for designing high-performance cathode materials in sodium-ion battery systems.