These results demonstrate that the sloping potential profile is due to the new redox activity with higher potential. In addition, many other dopants such as Li + , Zn 2+ , Cu 2+ , Fe 3+ , Ti 4+ , etc. can also induce sloping potential profiles in Ni and Mn-based layered oxides above 4.0 V. The dopants Li + , Zn 2+ , and Cu 2+ have been shown to demonstrate similar properties to that of Mg in relation to how they trigger oxygen redox in P-type and Ni-free Mn-based layered oxides for SIBs. It is therefore understandable that the sloping behavior is also related to the appearance of a new redox centre, i.e. 'O bound to Li/Zn/Cu'. Although there are a few reports that Fe or Ti can trigger oxygen redox, the Fe 3+ /Fe 4+ redox couple has been shown to exist in many layered oxides above 4.0 V, and Ti has been found to facilitate the oxidation of oxygen in layered oxides. These reports collectively indicate that the appearance of a sloping (remaining) high voltage plateau in the potential profiles are related to the presence (absence) of additional redox centres in Ni-Mn based layered oxides.