Boosting the electrochemical performance of P2-type Na0.5Mn0.95Ni0.05O2 by water soaking and post calcination

Although P2-type Na0.5Mn0.95Ni0.05O2 has a high theoretical specific capacity, its cut-off voltage often needs to be controlled below 4.0 V to avoid irreversible phase transformation (P2 to O2 or OP4) at high voltage and ensure the cycling stability, In this way, Na0.5Mn0.95Ni0.05O2 is difficult to demonstrate the advantage of high specific capacity. In this work, Na0.5Mn0.95Ni0.05O2 microspheres (NMNO) have been prepared by a solvothermal method, then treated with water soaking and post calcination to obtain P2-type Na0.5Mn0.95Ni0.05O2 with expanded Na+ layer spacing (P-NMNO). Between voltage window of 2.0 V-4.0 V, the P-NMNO delivers ultrahigh discharge capacities of 199.4, 170.8, 157.5, 142.3, 124.8, 105.4, and 99.0 mAh g-1 at 20, 50, 100, 200, 500, 800 and 1000 mA g-1, respectively. In contrast, NMNO only shows corresponding capacities of 129.2, 115.1, 106.6, 95.9, 80.3, 67.3, and 60.2 mAh g-1. What's more, the specific capacity of P-NMNO can still remain as 90.9 mA g-1 at 1000 mA g-1 after 200 cycles together with a high capacity-retention of 84.9 %. This work provides a new strategy to improve the electrochemical performance of Na0.5Mn0.95Ni0.05O2, especially for specific capacity.