In situ fabrication of porous-carbon-supported α-MnO2 nanorods at room temperature: application for rechargeable Li–O2 batteries

Lithium–O2 cells can be considered the “holy grail” of lithium batteries because they offer much superior theoretical energy density to conventional lithium-ion systems. In this study, porous carbon-supported MnO2 nanorods synthesized at room temperature were explored as an electrocatalyst for rechargeable Li–O2 cells. Both high-energy X-ray diffraction and X-ray absorption fine-structure analyses showed that the prepared MnO2 exhibited a tetragonal crystal structure (α-MnO2), which has proved to be one of the most efficient catalysts to facilitate the charging of the Li–O2 cell. Under the current synthetic approach, α-MnO2 was uniformly distributed onto the surface of a carbon support, without disrupting the porous structure at the surface of the carbon cathode. As a result, the as-prepared catalysts demonstrated good electrochemical behavior, with a capacity of ∼1400 mA h g−1 (carbon + electrocatalyst) under a current density of 100 mA g−1 (carbon + electrocatalyst) during the initial discharge. The charge potential was significantly reduced, to 3.5–3.7 V, compared with most of the reported data, which are above 4.0 V. The mechanism of the capacity fade with cycling was also investigated by analyzing the cathode at different states of discharge–charge by X-ray photoelectron spectroscopy.