Electrochemical properties of P2-Na2/3[Ni1/3Mn2/3]O2 cathode material for sodium ion batteries when cycled in different voltage ranges

P2-type Na2/3[Ni1/3Mn2/3]O2 cathode material has been synthesized via spray drying method and a two step solid state process. Electrochemical behavior of the prepared material as cathode material for sodium ion battery was investigated in different charge-discharge voltage ranges. The results indicated that the cycling performance of the P2-Na2/3[Ni1/3Mn2/3]O2 cathode greatly depended on the voltage window. The material showed excellent reversibility between 2.0 V and 4.0 V with reversible capacity of 86 mAh g−1 (0.1 C) and 77 mAh g−1 (1 C). XRD analyses indicated that crystal structure of the P2-type Na2/3[Ni1/3Mn2/3]O2 could be well maintained after long term cycling in 2.0-4.0 V. When the upper limiting voltage was increased to 4.5 V, the crystal structure of P2-Na2/3[Ni1/3Mn2/3]O2 was irreversibly damaged due to over extraction of Na+ in 4.0-4.5 V. On the other hand, when the cycling voltage range was between 1.6 V and 3.8 V, the discharge capacities increased to 135 mAh g−1 (0.1 C) and 108 mAh g−1 (1 C), respectively. However, the cycling stability in 1.6-3.8 V was not as excellent as that in 2.0-4.0 V. This maybe due to the lattice stress caused by the over insertion of Na+ in the structure at lower voltage.