Computational studies on magnesium spinel’s [MgY₂S₄ and MgY₂Se₄]

Materials Modelling Centre, University of Limpopo, Private Bag x1106, Sovenga, 0727, South Africa

^* Corresponding author: tibanekhumbulani01@gmail.com

Abstract

The need for novel battery cathode materials is growing every day, and an ongoing study on magnesium (Mg) has intensified due to its many advantages such as its abundance on earth, low cost, and ease of handling. Furthermore, Mg₂₊ has the advantage of doubling the overall charge per ion compared to Li₊ and boosting the energy density of a battery. The major challenge, is the identification of cathode materials that demonstrate capacities and voltages similar to lithium-ion systems. In this study, the first principle–based calculations were used to investigate the stability of discharge products for MgY₂S₄ and MgY₂Se₄ structures employing density functional theory (DFT) through VASP within the generalized gradient approximation (GGA) in the form of Perdew-Burke-Ernzerhof (PBE) exchange-correlation. The computed elastic constants indicate that the structures are mechanically stable. We found that MgY₂S₄ and MgY₂Se₄ structures are electronically stable semi-conductors with direct band gaps of 1.79 and 1.27 eV observed in the density of states, respectively. No negative vibrational frequencies are observed in all directions in the phonon dispersion curves, which indicates vibrational stability. The findings of this work aim to improve the production, research, and development of solid electrolyte magnesium-ion batteries.