Morphological and Crystalline Evolution of Nanostructured MnO2 and Its Application in Lithium–Air Batteries

Single-crystal α-MnO2 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 MnO2 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-MnO2 nanotubes exhibit much better stability than those made of α-MnO2 nanowires and δ-MnO2 nanosheet-based microflowers in both charge and discharge processes.