Evaluation of Spinel-Type Compounds as Potential Intercalation Hosts for Magnesium Batteries

Abstract

Given the growing demand for energy storage and the finite supply of lithium, magnesium batteries (MBs) are a feasible alternative. The crucial task is to discover high-energy-density positive electrode materials that can facilitate ion shuttling between the electrodes during battery operations with appropriate Mg²⁺ ion intercalation kinetics. In this work, for picking potential positive intercalation electrodes for MBs, we have systematically studied the electrochemical performance of the compounds with spinel structure MgM₂O₄ spanning a matrix of seven redox-active transition metal cations (Ti to Ni) using density functional theory (DFT) calculations. The key parameters that we must consider in modeling battery electrode materials are highlighted in this work. Our focus here is to compute the key parameters such as specific capacity, average (de)intercalation voltages, ionic mobilities, and dynamics of these materials. We also examine the volume change during charging and discharging, which gives an approximate idea about these materials’ cyclic performance and safety in MBs. The 0-K voltage profile for the electrochemical insertion–deinsertion of Mg²⁺ in MgM₂O₄ is projected to investigate the possible use of spinel compounds as cathode materials. The compositions based on Co and Ti show the highest voltages, 3.5 V, and lowest voltages, 2.1 V, respectively, in terms of average intercalation voltages; during Mg intercalation–deintercalation, M contributes to the redox behavior. The investigation’s most noteworthy finding is the high mobility of shuttling cations in spinel compounds. With a diffusion energy barrier of 0.4–0.65 eV, the migration of Mg²⁺-ion in MgM₂O₄ shows that its mobility is analogous to Li⁺-ions in conventional Li-ion battery cathodes. When all the studied properties of these seven materials are balanced, Cr- and Co-based spinel structures are good options among transition metals as they show high voltage and low diffusive energy barriers.