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

Abstract

In this work, α-NaMnO₂ has been synthesized first. And then, after reacting with water, α-NaMnO₂ translates into crystal water containing Na-birnessite with a large interlayer distance of 7.15 Å. The synthesized α-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 α-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.