Heteroatom anchoring to enhance electrochemical reversibility for high-voltage P2-type oxide cathodes of sodium-ion batteries

P2-type cathode has received extensive attention due to its faster Na⁺ diffusion and a high theoretical capacity in sodium-ion batteries (SIBs). However, undesirable phase transformations have induced dramatic capacity decay of SIBs during the cycling process. In this study, heteroatom anchoring through Cu/Mg dual doping is introduced into P2-type Na_0.67Ni_0.33Mn_0.67O₂ cathode to enhance high-voltage electrochemical reversibility and modulate interfacial Na⁺ kinetics. The as-prepared Na_0.67Ni_0.23Mg_0.05Cu_0.05Mn_0.67O₂ exhibits an outstanding capacity retention (83.4 % after 2000 cycles at 10 C) and rate performance (73 mAh g⁻¹ at 10 C, accounting for 58.7 % of that at 0.1 C) over the voltage range of 2.5–4.4 V. Intensive explorations further manifest that the modified mechanism of dual-ion doping strategy is attributed to the synergistic coupling effect of a substantial change in Na occupancy distribution and an increase in oxygen vacancy buffer. Thus, the optimized cathode expedites Na⁺ diffusion and reduces detrimental phase transformation, which favors high-rate performance and long-term cycling stability. This study develops a route to rationally design high-voltage cathode materials for SIBs.