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 Na0.67Ni0.33Mn0.67O2 cathode to enhance high-voltage electrochemical reversibility and modulate interfacial Na+ kinetics. The as-prepared Na0.67Ni0.23Mg0.05Cu0.05Mn0.67O2 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.