Probing Mg Migration in Spinel Oxides

Bayliss, R.; Key, B.; Gautam, G. S.; Canepa, P.; Kwon, B. J.; Lapidus, S. H.; Dogan, F.; Adil, A. A.; Lipton, A. S.; Baker, P. J.; Ceder, G.; Vaughey, J. T.; Cabana, J.

doi:10.1021/acs.chemmater.9b02450

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, 663–670 (2020).

BibTeX

@article{Bayliss2020probing,
  author  = {Bayliss, R. and Key, B. and Gautam, G. S. and Canepa, P. and Kwon, B. J. and Lapidus, S. H. and Dogan, F. and Adil, A. A. and Lipton, A. S. and Baker, P. J. and Ceder, G. and Vaughey, J. T. and Cabana, J.},
  title   = {{Probing Mg Migration in Spinel Oxides}},
  journal = {Chemistry of Materials},
  volume  = {32},
  pages   = {663--670},
  year    = {2020},
  doi     = {10.1021/acs.chemmater.9b02450}
}

Brief summary

Magnesium batteries with oxide electrodes could beat lithium-ion, but magnesium was thought to move too slowly through oxides. Combining experiments and calculations on three spinel oxides, we measure barriers for a magnesium hop as low as about 0.6 eV, low enough for working electrodes, and show that the real challenge is the chemical stability of the charged material.

Full 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.