This O redox process occurs at a slightly higher redox potential than that occurring when O is only bound to Ni, resulting in the observed sloping potential profile for the Mg-doped material. Although the dopants can induce different shapes in the high voltage region of the potential profiles, they are found to have a greater effect on the average voltage than on the cycling stability. This new finding underlines the complex interplay between structure, redox chemistry, and doping in Na layered oxides and provides an additional explanation towards understanding doping effects in layered oxides.