From alpha-NaMnO2 to crystal water containing Na-birnessite: enhanced cycling stability for sodium-ion batteries

In this work, alpha-NaMnO2 has been synthesized first. And then, after reacting with water, alpha-NaMnO2 translates into crystal water containing Na-birnessite with a large interlayer distance of 7.15 angstrom. The synthesized alpha-NaMnO2 exhibits a discharge capacity (126.4 mA h g(-1)) higher than that of the crystal water containing Na-birnessite (100.9 mA h g(-1)). However, the crystal water containing Na-birnessite exhibits a cycling stability higher than alpha-NaMnO2 owing to the larger interlayer distance of Na-birnessite with the crystal water in the interlayer. Therefore, an effective way to improve the cycling stability of this kind of material is by changing the interlayer distance.