High-capacity nanostructured manganese dioxide cathode for rechargeable magnesium ion batteries

Nanostructured [lambda]-MnO sub(2) and alpha -MnO sub(2) are investigated for use in rechargeable Mg ion battery (MIB) cathodes. In order to prepare nanosized particles, the manganese dioxides are prepared by the acid treatment of spinel MgMn sub(2)O sub(4) synthesized using the Pechini method. X-ray diffraction analysis indicates that the resulting MnO sub(2) consists of multiple phases, [lambda]-MnO sub(2), alpha -MnO sub(2), and beta -MnO sub(2), depending on the leaching time in acid solution. Upon the first charge-discharge cycle in acetonitrile electrolyte, the [lambda]-MnO sub(2) based electrode shows larger reversible capacity of ~330 mAh g super(-1) compared to an electrode containing a large amount of alpha -MnO sub(2). This enhanced capacity is associated with the facile charge-transfer reaction of Mg ions at the MnO sub(2)/electrolyte interfaces. The capacity fading of MnO sub(2) in different electrolytes is also discussed in terms of the formation of a surface layer at the electrode/electrolyte interface during the charging process.