Stabilizing O3-type layered oxide cathodes through Zn doping for high-energy sodium-ion batteries

In this work, we investigate through a combined experimental and computational approach the impact of partially substituting Ni with Zn in O3-type NaNi 0.33-x Zn x Fe 0.17 Mn 0.5 O 2 (x = 0, 0.05) layered cathodes, a representative high-capacity system for sodium-ion batteries. Owing to its electrochemical inactivity, Zn 2+ is incorporated into the layered structure without altering the rhombohedral R-3m symmetry of the as-prepared material. Experimental characterization and first-principles calculations suggest that the presence of Zn–O bonds can contribute to limiting transition-metal migration into the Na layers and to mitigating lattice distortion during Na extraction, thereby supporting a more reversible O3–P3 phase transition. Zn doping improves the local electronic environment of Fe, modulating the Fe 3+ /Fe 4+ redox activity. Electrochemical measurements confirm that Zn doping reduces electrode polarization and contributes to cycling stability, even within the extended 2.0–4.2 V window where structural degradation is typically severe. These results indicate that Zn substitution is an effective strategy to improve the structural and electrochemical stability of O3-type layered cathodes for advanced NIBs.