Structural and electronic properties of β-MnO₂ nanoclusters

University of Limpopo, School of Physical and Mineral Sciences, Materials Modeling Centre, Private Bag x1106, Sovenga, 0727

^* Corresponding author: phalamasoga@gmail.com

Abstract

Pyrolusite (β-MnO₂) was investigated for potential use in energy storage devices due to its promising properties for cathode materials in rechargeable lithium-ion batteries. A combination of evolutionary algorithm search techniques and density functional theory techniques were used to determine the structural stabilities of the β-MnO₂ nanoclusters on the energy landscape. However, pyrolusite suffers from some structural defects and impurities that hinder its optimal use. The predicted order of stability for the MnO₂ nanoclusters correlates with isostructural TiO₂. There is an improvement in the stability and electrical conductivity of the nanoclusters as compared to their β-MnO₂ bulk counterparts. The cobalt doped nanoclusters showed a preference toward circular compact bonding patterns. The band-gap energy revealed that the nanoclusters have a metallic characteristic behaviour with narrow band gap energies, indicating their good conductive properties. Cobalt doping was shown to improve the structural properties of the nanoclusters based on the decreased bond lengths and more spherical bond angles. Moreover, it also succeeded in improving the conductivity of the nanoclusters based on the reduced Mulliken and Hirshfeld partial charges. The electronic charge density differences of the cobalt doped β-MnO₂ nanoclusters displayed a prevalence of the weaker ionic bonding instead of the preferred stronger covalent bonding. This shows the limited effectiveness of cobalt as a dopant.