Solvent Effects on the Reversible Intercalation of Magnesium-Ions into V₂O₅ Electrodes

The choice for solvents in electrolyte solutions for non-aqueous magnesium batteries is currently limited to ethers. However, the scientific community regularly uses acetonitrile (ACN) based electrolyte solutions as model systems in order to characterize new cathode materials for rechargeable Magnesium batteries. In this study, we demonstrated the effect of dimethoxyethane (DME), an important solvent for rechargeable magnesium systems, on the reversible intercalation of Mg²⁺ cations into thin, monolithic V₂O₅ films. The effect of DME on the intercalation kinetic have been examined via chronopotentiometry, galvanostatic and galvanostatic intermittent titration (GITT) measurements. In addition, we explored basic scientific questions related to the structure of ACN:DME based electrolyte solutions via Raman spectroscopy and surface chemistry of V₂O₅/Mg(ClO₄)₂/ACN:DME systems via X-ray photoelectron spectroscopy. We found that addition of DME to the Mg(ClO₄)₂/ACN solution results in replacing the ACN-Mg²⁺ cation by the more thermodynamically stable 3DME-Mg²⁺ solvate structure. We also found that the DME-Mg interaction forms stable solution structures that kinetically slow down the insertion of the Mg²⁺ cations into V₂O₅, compared with the less coordinated situation in solutions based solely on ACN.