Bulk modification engineering of O3-NaNi_0.5Mn_0.5O₂ layered cathode through dual-doping and synergism enables stable cycling of sodium-ion batteries

The O3-type NaNi_0.5Mn_0.5O₂ is a promising cathode material for sodium-ion batteries, however, it faces challenges such as complex structural changes, low sodium-ion diffusion rates, and irreversible oxygen loss, which result in lower initial capacity and rapid capacity decay. In this study, a bulk modification engineering is proposed to enhance the phase stability, improve sodium-ion diffusion rates, and reduce lattice oxygen loss through a Cu/Li co-doping strategy. Compared to O3-type NaNi_0.5Mn_0.5O₂, the Cu/Li tailored NaNi_0.4Mn_0.5Cu_0.08Li_0.02O₂ demonstrated improved electrochemical performance, with an initial capacity of up to 218.7 mAh g⁻¹. After 200 cycles at a 1C rate, the capacity retention of the half-cell increased from 39.3 % to 63.8 %. This work illustrates that the co-doping strategy effectively and reliably stabilizes the material structure and enhances the performance of layered cathodes in sodium-ion batteries.