High capacity sodium-rich layered oxide cathode for sodium-ion batteries

Sodium-ion batteries have attracted significant recent attention currently considering the limited available lithium resource. However, the energy density of sodium-ion batteries is still insufficient compared to lithium-ion batteries, mainly because of the unavailability of high-energy cathode materials. In this work, a novel sodium-rich layered oxide material (Na₂MnO₃) is reported with a dynamical stability similar to that of the Li₂MnO₃ structure and a high capacity of 269.69 mA·h·g¹, based on first-principles calculations. Sodium ion de-intercalation and anionic reaction processes are systematically investigated, in association with sodium ions migration phenomenon and structure stability during cycling of Na_xMnO₃ (1 ≤ x ≤ 2). In addition, the charge compensation during the initial charging process is mainly contributed by oxygen, where the small differences of the energy barriers of the paths 2c→4h, 4h→2c, 4h→4h, 2c→2b, and 4h→2b indicate the reversible sodium ion occupancy in transitional metal and sodium layers. Moreover, the slow decrease of the elastic constants is a clear indication of the high cycle stability. These results provide a framework to exploit the potential of sodium-rich layered oxide, which may facilitate the development of high-performance electrode materials for sodium-ion batteries.