Co-operative Interaction of Multiple Ions for P2-Type Sodium-Ion Battery Cathodes at High-Voltage Cyclability

Layered P2-type Na_0.67Ni_0.33Mn_0.67O₂ (NNMO) is regarded as a viable cathode material because of its open structure, high theoretical capacity, and simplicity in preparation. However, it suffers from intrinsic lattice distortion, complex phase transitions, and severe Na⁺/vacancy ordering severe issues. In this study, the synthesized Na_0.78Li_0.05Cu_0.05Ni_0.25Mn_0.6Ti_0.05O₂ (NLCNMTO) cathode material introduces the substitution of Li, Cu, and Ti for Ni and Mn. Through the synergistic effect of multiple ions, the structural stability is improved and the Na⁺/vacancy ordering and phase transition are suppressed at high voltage. NLCNMTO materials have better ionic conductivity and stronger TM–O covalent bonds, which improves the composites’ ionic diffusion rate and structural stability. It is stabilized in the P2 phase over a voltage range of 2–4.5 V with good cycling stability and multiplicative performance. This study provides a possible multi-ion codoping design for advanced SIBs cathode materials with optimized high-voltage activity as well as excellent structural stability.