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.
