On the solvation structures formed in conditioning-free MMAC-based electrolytes: A theoretical–experimental spectroscopic insight of interest to Mg battery area

The 2.39:1 Mg:MgCl2:AlCl3 (MMAC)-tetrahydrofuran (THF) and 1:1.22 MMAC-diethylene glycol dimethyl ether (G2) electrolytes, which have been already investigated by electrochemical measurements, are studied in the current work by using experimental vibrational spectroscopy allied to ab initio molecular dynamics (AIMD) simulations of spectra. Raman data are practically identical to the 2:1 MgCl2:AlCl3 (MACC)-THF and 3:5 MACC-G2 binary systems, except for a 330 cm−1 band, commonly assigned to [AlCl3(THF)1-2] and/or [AlCl2]+, which is absent for the THF-based ternary system. Subtle changes are also seen in the far-IR spectra, where a band at around 315 cm−1 shows strong dependence on the MgCl2 content and so may be associated to the [Mg2(μ-Cl)3]+ dimer. The monomeric species, [MgCl]+, is also observed in both electrolytes by means of IR bands at 270–285, 300 and 325–330 cm−1. The varied amounts of monomer and dimer seem to be related to the electrochemical activities determined for these ternary systems.