A new P2-structured oxide Na0.8Ni0.4Mn0.6O2 was synthesized using a solid reaction method in which Na2CO3,MnO2 and NiO were used as starting materials.This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions,including good rate capability and good cycle performance at both room temperature and elevated temperature.It displays two apparent voltage plateaus at about 3.6 and 3.3 V,and its discharge capacity reaches 92 mAh.g-1 at 0.1C in the voltage range of 2.0-4.0 V.At 1.0C,its discharge capacity reaches 85.3 mAh·g-1.After 80 cycles at different current rates,the as-prepared sample exhibits good capacity retention.At elevated temperature of 55 ℃,the discharge capacity remains the same at low current rate of 0.1C,but at high current rate of 1.0C,the discharge capacity is a little lower than that at room temperature.