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

Nanostructured λ-MnO₂ and α-MnO₂ 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 MgMn₂O₄ synthesized using the Pechini method. X-ray diffraction analysis indicates that the resulting MnO₂ consists of multiple phases, λ-MnO₂, α-MnO₂, and β-MnO₂, depending on the leaching time in acid solution. Upon the first charge-discharge cycle in acetonitrile electrolyte, the λ-MnO₂ based electrode shows larger reversible capacity of ∼330 mAh g^-1 compared to an electrode containing a large amount of α-MnO₂. This enhanced capacity is associated with the facile charge-transfer reaction of Mg ions at the MnO₂/electrolyte interfaces. The capacity fading of MnO₂ in different electrolytes is also discussed in terms of the formation of a surface layer at the electrode/electrolyte interface during the charging process.