In summary, Mg and Sc have been doped into O3-NaNi 0.5 Mn 0.5 O 2 using a solid-state and high-temperature calcination method. The dopants both show a largely positive enhancement of the cycling stability in a voltage range of 2.5-4.4 V compared to the undoped material. A comparison of the electrochemical, structural, redox properties, and potential shapes for the undoped and doped materials are shown in Table .