P2-phase Na0.74CoO2 cathode material prepared by a solid-state method exhibits the specific discharge capacity of 107mAhg−1 at 0.1C with good cycling performance for rechargeable sodium ion batteries. The voltage polarization between charging and discharging at 0.1C rate is about 150–250mV and the coulombic efficiency in each cycle is about 89%. The expansion and compression in c-axis of the Na x CoO2 unit cell during the Na intercalation/deintercalation is revealed by ex situ XRD. XPS and in situ XAS data directly confirm that deintercalation/intercalation of Na ions from/into the layered structure proceeds with the Co3+/Co4+ redox reaction.