AUTHOR=Matsui Masaki , Kuwata Hiroko , Mori Daisuke , Imanishi Nobuyuki , Mizuhata Minoru 

TITLE=Destabilized Passivation Layer on Magnesium-Based Intermetallics as Potential Anode Active Materials for Magnesium Ion Batteries

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00007

DOI=10.3389/fchem.2019.00007

ISSN=2296-2646

ABSTRACT=<p>Passivation of magnesium metal anode is one of the critical challenges for the development of magnesium batteries. Here we investigated the passivation process of an intermetallic anode: Mg<sub>3</sub>Bi<sub>2</sub> synthesized by solid-state and thin film process. The Mg<sub>3</sub>Bi<sub>2</sub> composite electrode shows excellent reversibility in magnesium bis(trifluoromethansulfonylamide) dissolved in acetonitrile, while Mg<sub>3</sub>Sb<sub>2</sub>, which has same crystal structure and similar chemical properties, is electrochemically inactive. We also fabricated the Mg<sub>3</sub>Bi<sub>2</sub> thin film electrodes, which show reversibility with low overpotential not only in the acetonitrile solution but also glyme-based solutions. Surface layer corresponding to the decomposed TFSA anion is slightly suppressed in the case of the Mg<sub>3</sub>Bi<sub>2</sub> thin film electrode, compared with Mg metal. Comparative study of hydrolysis process of the Mg<sub>3</sub>Bi<sub>2</sub> and the Mg<sub>3</sub>Sb<sub>2</sub> suggests that the both intermetallic anodes are not completely passivated. The bond valence sum mapping of the Mg<sub>3</sub>Bi<sub>2</sub> indicates that the fast Mg<sup>2+</sup> diffusion pathway between 2<italic>d</italic> tetrahedral sites is formed. The electrochemical properties of the Mg<sub>3</sub>Bi<sub>2</sub> anode is mainly due to the less passivation surface with the fast Mg<sup>2+</sup> diffusion pathways.</p>