Compared to the undoped material, the Mg and Sc doped materials exhibit much smoother charge/discharge curves below 4.0 V. In the high voltage region up to 4.4 V, significant differences between different materials were observed. There is a long and flat high voltage plateau for the P2-NaNMO sample, which can deliver a capacity of about 70 mAh g -1 (out of 150 mAh g -1 for the full charge capacity in the 1 st cycle). P2-NaS0.10NMO has a similar high voltage plateau, but it is shorter than that of the undoped P2-NaNMO, and only delivers a capacity of about 45 mAh g -1 (out of 136 mAh g -1 for the full charge capacity in the 1 st cycle). In contrast, the Mg-doped material shows a sloping potential profile in the high voltage region, and the corresponding dQ/dV curve shows the lowest signal intensity above 4.0 V among the investigated materials, indicating that Mg doping suppresses the high voltage plateau more completely. The Sc-doped material shows electrochemical behavior similar to that of the undoped P2-NaNMO material, which also shows a high intensity peak above 4.0 V in the dQ/dV curve. These observations demonstrate that the two dopants have different roles in the electrochemical reaction. During long-term cycling, it can be seen that P2-NaM0.10NMO