Synergistic Disorder-Driven and Framework-Locking Mechanism Enabling High-Voltage Stability of Sodium-Ion Layered Oxide Cathodes

The high-voltage stability of P2-type layered oxide cathodes for sodium-ion batteries is closely related to their intrinsic structural characteristics. However, complex phase transitions and structural degradation at high voltage lead to rapid capacity decay. Here, a synergistic Li/Nb co-doped P2-type layered cathode is developed. Li doping disrupts Na+/vacancy ordering and redirects the high-voltage phase-transition pathway from a deleterious P2→O2 transition toward a milder Z-like O/P intergrowth evolution. Nb incorporation preserves this pathway while further reinforcing the transition-metal coordination environment. This dual modification suppresses local structural distortion, alleviates lattice strain, and mitigates irreversible oxygen release. Consequently, Na0.67Ni0.21Li0.11Mn0.63Nb0.05O2 exhibits 93.1% capacity retention after 100 cycles at 2C within 2.0–4.3 V. This work elucidates how elemental co-doping regulates local coordination and structural evolution during charge and discharge, offering a strategy for stabilizing P2-type layered oxide cathodes under high-voltage operation.