Synthesis and Electrochemical Properties of Sodium Manganese-based Oxide Cathode Material for Sodium-ion Batteries

Hexagonal P2-structure sodium manganese-based NaLi0.2Mn0.8O2 oxide is successfully synthesized by a simple conventional solid-state reaction method. XRD analysis reveals that the NaLi0.2Mn0.8O2 material has layered structure, space group P63/mmc, and lattice parameters of a = 2.8616 Å, and c = 11.0659 Å. Lithium ions can stabilize the P2-structure of sodium manganese-based NaxMnO2 oxides even though the mole ratio of alkali metals to transition metal is as high as 1.5. The NaLi0.2Mn0.8O2 material has a high initial discharge capacity of 241 mAh g−1 between 1.5–4.5 V at a current density of 26.6 mA g−1. The structure of the NaLi0.2Mn0.8O2 material is stable over a wide range of sodium concentrations during the charge-discharge process, and capacity retention is 78% after 40 cycles.