Probing Mg Migration in Spinel Oxides

R. Bayliss, B. Key. G. S. Gautam, P. Canepa, B. J. Kwon, S. H. Lapidus, F. Dogan, A. A. Adil, A. S. Lipton, P. J. Baker, G. Ceder, J. T. Vaughey and J. Cabana; Chem. Mater. 32 (2), 663-670 (2020).

Abstract

Mg batteries utilizing oxide cathodes can theoretically surpass the energy density of current Li-ion technologies. The absence of functional devices so far has been ascribed to impeded Mg2+ migration within oxides, which severely handi-caps intercalation reactions at the cathode. Broadly, knowledge of divalent cation migration in solid frameworks is surprisingly deficient. Here we present a combined experimental and theoretical study of Mg migration within three spinel oxides, which reveal critical features that influence it. Experimental activation energies for a Mg22+ hop to an adjacent vacancy, as low as ~600 meV, are reported. These barriers are low enough to support functional electrodes based on the intercalation of Mg2+. Subsequent electrochemical experiments demonstrate that significant demagne-siation is indeed possible, but that challenges instead lie with the chemical stability of the oxidized states. Our find-ings enhance the understanding of cation transport in solid structures and renew the prospects of finding materials capable of high density of energy storage.