This work elucidated the structure and electrochemical performance of the layered cathode material Na _xMn _0.5Co _0.5O ₂ (NMC) with x~1 calcined at 650, 800 and 900 ^oC. XRD diffraction indicated that the NMC material possessed a phase transition from P3- to P2-type layered structure with bi-phasic P3/P2 at medium temperature. The sodium storage performance was evaluated by constant current charging/discharging. Specifically, P2-NMC exhibits the highest initial capacity of 156.9 mAh.g ^-1 with capacity retention of 76.2% after 100 cycles, which is superior to the initial discharge capacity is only 149.3 mAh.g ^-1 and severe capacity fading per cycle of P3-NMC, indicating high robust structure stability by calcined at the higher temperature. Additionally, the best performance of P2-NMC also demonstrated by the high-rate capability that delivered a capacity of 50 mAh.g ^-1 at charge/discharge rate up to 10C. The sodium diffusion coefficient of Na ⁺ ions into the P2-type layered structure obtained by Cyclic Voltammetry (CV) was in the range of 10 ⁻¹³–10 ⁻¹² cm ².s ⁻¹, which is inferior to the others. However, the structure stability of P2 phase contributed to the best prerformance in sodium-ion half-cell.