First-Principles Investigation of MoS2-MXene Heterostructures as Cathodes in Magnesium Ion Batteries

Abstract

Technological advancements in the field of energy storage are crucial for an efficient and large-scale use of the renewable energy sources. With the Lithium-ion batteries reaching their maximum theoretical limits of capacity, multivalent ion batteries have attracted attention. High charge storage capacity of the Magnesium anode, multivalency of the Magnesium ion, the high reduction potential, and the large abundance of Magnesium in Earth’s crust (2.1 %) are the main advantages of Magnesium-Ion Batteries (MgIBs). Sluggish diffusion of Magnesium atoms into intercalation cathodes and low working voltages offered by cathodes are two of the important challenges in improving the performance of MgIBs. In this work, we propose to use the heterostructures of two-dimensional materials as cathodes in MgIBs. Layered two-dimensional materials have a distinct advantage over the other materials as they can provide enormous area for adsorption and the large interlayer spacings can permit the diffusion of atoms. We have studied, using first-principles density functional theory calculations, the application of two-dimensional heterostructure of MoS2 and Ti2CO2 as possible cathode materials in MgIBs. Motivation for integration of MoS2 and Ti2CO2 is to exploit their individual properties crucial for improving the MgIB cathodes. Previous studies reveal that MoS2 can allow fast diffusion of Mg atoms on its surface whereas, Ti2CO2 can offer large gravimetric capacity. We thoroughly studied energetics of Mg adsorption on MoS2 and Ti2CO2, and also compared their diffusivity using phenomenological models. We have estimated that high intercalation energy (3.52 eV for 11% and 2.63 eV for 100% intercalation sites occupied) and slowly varying discharge curve can be obtained using MoS2-Ti2CO2 as MgIB cathode. Further, interlayer distance tuning of the heterostructure can facilitate much faster diffusion (energy barrier less than 0.1 eV) of Mg through interlayer spacing. Experimental studies are required to gain further insights to improve the design of cathode. We have also pointed out the discrepancy between the theoretical estimate of the voltage of MgIB with MoS2 cathode and Mg bulk anode and observed voltage for the same battery system, which needs to be addressed.