Morphological and crystalline evolution of nanostructured MnO2 and its application in lithium--air batteries.

Single-crystal α-MnO(2) nanotubes have been successfully synthesized by microwave-assisted hydrothermal of potassium permanganate in the presence of hydrochloric acid. The growth mechanism including the morphological and crystalline evolution has been carefully studied with time-dependent X-ray diffraction, electron microscopy, and controlled synthesis. The as-synthesized MnO(2) nanostructures are incorporated in air cathodes of lithium--air batteries as electrocatalysts for the oxygen reduction and evolution reactions. The characterization reveals that the electrodes made of single-crystalline α-MnO(2) nanotubes exhibit much better stability than those made of α-MnO(2) nanowires and δ-MnO(2) nanosheet-based microflowers in both charge and discharge processes.