Solvation of Magnesium Ion in Triglyme-Based Electrolyte Solutions

We report here structural study on solvation of Mg 2+ ion in triglyme (G3)-based solutions applying as a novel electrolyte for rechargeable Mg batteries. In Mg(TFSA) 2 /G3 electrolyte solutions (TFSA = bis(trifluoromethanesulfonyl)amide), we found from Raman spectroscopy that Mg 2+ ion is solvated with two G3 molecules to form [Mg(G3) 2 ] 2+ complexes. No direct coordination of TFSA – anion to Mg 2+ ion occurs in the solutions with the salt concentrations c Mg = 0–1.60 M. The geometries and interaction energies for the [Mg(G3) 2 ] 2+ were evaluated by DFT calculations and indicated that G3 molecules in the most stable complex act as a tridentate ligand, i.e., octahedral [Mg(tri-G3) 2 ] 2+ . However, the Raman spectra implies that [Mg(tri-G3) 2 ] 2+ coexists with [Mg(tetra-G3) (bi-G3)] 2+ in the solutions where tetra-G3 and bi-G3 are G3 molecules acting as tetra- and bidentate ligands, respectively, in the solvation sphere. The Walden plots indicated that the dissociativity (or ionicity) of Mg(TFSA) 2 in G3 solutions increases with increasing c Mg, which is opposite to conventional organic electrolyte solutions but is similar to the LiTFSA/glyme solutions.