Na 0.67 Mn 1x Mg x O 2 (0 ≤ x ≤ 0.2): A High Capacity Cathode for SodiumIon Batteries

Earthabundant Na 0.67 [Mn 1xMg x]O 2 (0 ≤ x ≤ 0.2) cathode materials with the P2 structure have been synthesized as positive electrodes for sodiumion batteries. Na 0.67 MnO 2 exhibits a capacity of 175 mAh g 1 with good capacity retention. A Mg content of 5 % is sufficient to smooth the charge/discharge profiles without affecting the capacity, whilst further increasing the Mg content improves the cycling stability, but at the expense of a lower discharge capacity (~ 150 mAh g 1Na 0.67 Mn 0.8 Mg 0.2 O2). It was observed that the