P2-phase Na0.74CoO2 cathode material prepared by a solid-state method exhibits the specific discharge capacity of 107 mAh g(-1) at 0.1 C with good cycling performance for rechargeable sodium ion batteries. The voltage polarization between charging and discharging at 0.1 C rate is about 150-250 mV and the coulombic efficiency in each cycle is about 89%. The expansion and compression in c-axis of the NaxCoO2 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. (C) 2012 Elsevier Ltd. All rights reserved.