Structure of Magnesium Chloride Complexes in Ethereal Systems: Computational Comparison of THF and Glymes as Solvents for Magnesium Battery Electrolytes

The structure of the electrolyte is crucial for the performance of rechargeable magnesium batteries. Doubly charged cations interact much stronger with both anions and solvent molecules, forming different size clusters. Here, we apply DFT calculations to investigate salt solvation by altering the first solvation shell of the magnesium-chloride complexes in different ethereal solvents: tetrahydrofuran, monoglyme, diglyme, triglyme and tetraglyme. The analysis was performed by looking for the most stable structures, considering mono-, di- and trimeric clusters of MgxCly. The determination of clusters geometries, together with their energies, resulted in a comprehensive picture of the thermodynamically preferred state of the electrolyte, and allowed for a simple assessment of the electrochemical activity of the electrolyte. Our analysis shows that clustering is beneficial for desolvation of magnesium from the cluster, but causes overpotentials due to hindered electron transfer.