Abstract:

Nanowall arrays of hydrous manganese dioxide MnO₂·0.5H₂O were deposited on cathodic substrates by the potentiostatic method from a mixed aqueous solution of manganese acetate and sodium sulfate, and the Li⁺ ions intercalation properties of such nanowall arrays were studied. The deposition was induced by a change of local pH resulting from electrolysis of H₂O. Composition of this new nanowall structure was investigated by means of combined XRD, XPS, and TGA and determined to be hydrous manganese dioxide. SEM study revealed that the MnO₂·0.5H₂O nanowall arrays were homogeneous across the entire substrate of top thicknesses that varied from 50 to 100 nm with identical depth. The nanowall arrays of hydrous manganese dioxide exhibited an initial capacity of 270 mAh/g with a reversible capacity maintained at 220 mAh/g at the 50th charge/discharge cycle in the Li⁺ ions intercalation capacity measurement at a high charge/discharge rate of 0.1 mA/cm² (C/2, 76 mAh/g). This greatly enhanced Li⁺ ions intercalation capacity is ascribed to the large active surface area of the nanowall arrays and a short facile diffusion path for Li⁺ ions. The nanowall arrays of hydrous manganese dioxide also displayed an improved cyclic stability attributed to the reduced strain accumulated in these nanostructures during Li⁺ ions intercalation.