Glyme Solvent Decomposition on Spinel Cathode Surface in Magnesium Battery

Abstract

The cathode performance is critical for developing a magnesium rechargeable battery, and spinel oxides MgM2O4 (M = Mn/Fe/Co) show promise. However, (de)magnesiation and oxidative electrolyte decomposition are major issues. In this study, we investigated the microscopic mechanisms of dimethoxyethane (DME) oxidative decomposition on MgM2O4 using density functional theory calculations. The study shows that demagnesiation promotes decomposition, and DME is most likely to decompose on MgMn2O4 during charging compared to that on MgFe2O4 and MgCo2O4. Density of states analysis reveals that the experimentally observed reactivity of MgMn2O4 is due to the closeness in energy between the highest occupied molecular orbital of DME and the valence band maximum of MgMn2O4. Moreover, the fragmentation of DME occurs first, making oxidation easier. The oxidation potential order, Mn (3.05 V) < Co (3.27 V) < Fe (3.59 V), observed in the cyclic voltammograms, matches the calculated charge potentials, which has a certain effect on the DME decomposition.