A Theoretical Investigation of Vanadium-Based Cathodes in Magnesium-Ion Battery

Lithium-ion battery (LIB) technology, first commercialized in 1991 by Sony, has been explored extensively to accomplish many achievements in energy supply throughout past decades due to its high energy density and low self-discharge. Nevertheless, there are still challenges with LIB in cost and scarcity. In addition, the effort of using metal lithium as an anode to increase capacity compared to graphite is limited by the dendrite formation during deposition of Li-ion, which results in problematic and unsafe operation. Magnesium-ion battery (MIB), an alternative to LIB, has received huge interest in the field due to magnesium’s higher abundance on Earth’s crust, less expensive, a provision of high capacity on the account of two electrons transfer and the negligible dendrite formation on the anode compared to lithium. Despite that, one of the main challenges to MIB technology is the poor cathode cyclability caused by sluggish kinetics of Mg-ion resulting from the high charge density at most cathodes, which can affect the rate capability of the battery. In this work, we are looking at several vanadium oxides, one of the well-known cathode materials: V₂O₅, LiV₃O₈, and V₂(PO₄)₃. These materials have been widely studied in LIB showing great performance during cycling due to its layered and stable structure which indicates a promising material for improving the cathode’s cyclability and the battery’s rate capability for MIB. Here, we used density function theory (DFT) to predict the theoretical voltages and energy densities of MIB using the magnesium metal anode and the studied vanadium-based cathodes to compare with LIB technology. We found that the MIB’s performance resulted in lower voltage but can be compensated by higher capacities in comparison to LIB; as a result, the energy densities of the two batteries can be commensurable. Furthermore, we constructed convex hull phase diagram to predict the process of intercalating Mg-ions into the studied cathodes and then predicted the voltage profile to study the phase boundaries which can affect the kinetics of intercalating ions within these cathodes in MIB. The result found that V₂O₅ and V₂(PO₄)₃ were developing phase boundaries during intercalation of Mg-ions while the flat voltage profile of LiV₃O₈ cathode looks more desirable for the kinetics of intercalating ions. Then, we will further investigate the kinetics characteristics of these vanadium-based cathodes by predicting the ionic conductivity and electrical conductivity which contribute greatly to the rate capability.