Atomic-scale Modelling of Magnesium Battery Electrodes

Magnesium batteries are the most promising alternative to lithium ion batteries towards green energy transition due to their relatively high volumetric capacity, availability of Mg and low safety concerns. However, the formation of passivation layer, sluggish ion kinetics and poor ductility of Mg remains a major challenge limiting the development and application in energy storage devices. The thesis presents four investigations designed to understand and develop suitable electrode materials for Mg batteries, addressing the core issues inhibiting their development.
First, a density functional theory (DFT) screening is performed to identify the dopants that enhance the ductility of the Mg anode. The dopants were selected after careful consideration of their ability to improve ductility, stability when alloyed with Mg, and low propensity for surface migration to prevent impact on electrochemical performance. The study identifies 12 dopants that can be alloyed with Mg for battery applications and also suggests a commercial alloy, WE43, as an anode for Mg batteries.
Second, a rigorous phase space search is carried out using DFT based cluster expansion to investigate the phases that form in Sn-based anode during charging and discharging of battery. Anodes based on Sn and its Mg intermetallics have been proposed as a potential solution to mitigate the passivation layer formation. In line with previous experiments, our findings imply that Sn and Mg2_Sn will be the only phases formed during battery operation, and we considered three routes for the transformation from Mg₂Sn to Sn.
Third, a detailed study is performed to understand the charge transport mechanism in the Mg-S battery cathode, with a particular emphasis on the discharge end products MgS and MgS₂, which limit reversible Mg
deposition. The study assesed several possible defects in these materials and identified the dominant defects that contribute to charge transport. Additionally, the charge transport under non-equilibrium conditions during practical battery operation is also studied using ab-initio molecular dynamics.
Fourth and the final project investigated the structural properties of disordered pyroborate MgMnB₂O₅ cathode. The study predicted the disorder in the material at different level of magnesiation. Despite having disorder, it is also observed that the material exhibits a specific pattern of cation occupation on fully magnesiation. Structural insights of this material at different level of magnesiation serve as starting point for further study on ion kinetics.
The findings in this thesis provide atomic-level insights into the properties of potential anode and cathode materials for magnesium batteries. The presented results will be able to compliment the researches ongoing world-wide to develop practical magnesium batteries.