After 200 cycles, the cycling stability of both of the doped compounds is significantly improved compared to the undoped materials, where the capacity retention of O3-NaMNMO and O3-NaSNMO is 49% and 54%, respectively. These show a marked improvement over the almost complete capacity loss (~100%) of O3-NaNMO without doping over the same number of cycles. Interestingly, although the two doped materials show similar capacity retention during long-term cycling, they show stronger differences in their average charging voltages (see Figure ). The Mg-doped material exhibits the largest value in the average charging voltage among the three materials in the first cycle due to its sloping potential profile, and the underlying reason is illustrated in Figure . In the following several cycles, the Mg-doped material also shows higher values in average voltage than the Sc-doped material. These results indicate that the two dopants play different roles in stabilizing the electrochemical properties of O3-NaNMO.