Layered P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 was successfully synthesized through a facile sol-gel method and subsequent heat treatment. Resulting from different phase transformation and sodium ion diffusion rates, its electrochemical performance is highly related to the cut-off voltage and the electrolyte used. When the cut-off voltage is set up to 4.5 V or lowered to 1.5 V, capacity fade happens due to the occurrence of P2-O2 transformation and electrolyte decomposition or the redox reaction of the Mn 4+ /Mn 3+ ionic pair and P2-P2′ transformation. The electrode maintained 89.0 mA h g -1 with good cycling stability and excellent structural preservation between 4.0 and 2.0 V. The capacity retention is 71.2% even after 1200 cycles at 10C. It can be expected that P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is very promising as a cathode material for sodium ion batteries.