Electrochemical properties of P2-type Na2/3Ni1/3Mn2/3O2 plates synthesized by spray pyrolysis process for sodium-ion batteries

P2-type Na2/3Ni1/3Mn2/3O2 plates with homogeneous composition and regular morphology are prepared by spray pyrolysis. The rhombohedral P3-Na2/3Ni1/3Mn2/3O2 microspheres formed by one-pot spray pyrolysis transform into hexagonal P2-Na2/3Ni1/3Mn2/3O2 plates after post-treatment at temperatures between 800 and 1000 °C. The mean size and thickness of P2-Na2/3Ni1/3Mn2/3O2 plates obtained after post-treatment at 900 °C are 2.2 μm and 550 nm, respectively. The initial discharge capacities of P2-Na2/3Ni1/3Mn2/3O2 plates formed at 800, 900, and 1000 °C at a current rate of 0.1C are 69, 86, and 80 mA h g−1, respectively, while the discharge capacities after 200 cycles are 68, 80, and 76 mA h g−1, respectively. However, the discharge capacities of P3-Na2/3Ni1/3Mn2/3O2 powders decrease from 62 to 50 mA h g−1 after 200 cycles. P2-Na2/3Ni1/3Mn2/3O2 plates show low charge-transfer resistance and also exhibit better rate performance than P3-Na2/3Ni1/3Mn2/3O2 powders.