Abstract
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: Mg3Bi2 synthesized by solid-state and thin film process. The Mg3Bi2 composite electrode shows excellent reversibility in magnesium bis(trifluoromethansulfonylamide) dissolved in acetonitrile, while Mg3Sb2, which has same crystal structure and similar chemical properties, is electrochemically inactive. We also fabricated the Mg3Bi2 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 Mg3Bi2 thin film electrode, compared with Mg metal. Comparative study of hydrolysis process of the Mg3Bi2 and the Mg3Sb2 suggests that the both intermetallic anodes are not completely passivated. The bond valence sum mapping of the Mg3Bi2 indicates that the fast Mg2+ diffusion pathway between 2d tetrahedral sites is formed. The electrochemical properties of the Mg3Bi2 anode is mainly due to the less passivation surface with the fast Mg2+ diffusion pathways.
Highlights
Beyond Li-ion batteries have been widely investigated last decade (Larcher and Tarascon, 2015)
Since the X-ray photoelectron spectroscopy (XPS) results only provide the composition and the oxidation state of the elements, here we investigated the stability of the passivation layer on the Mg3Bi2 and the Mg3Sb2 by storing them in ambient atmosphere and water
We investigated the electrochemical properties of the magnesium-based intermetallic compounds as alternative anode active material for magnesium batteries
Summary
Beyond Li-ion batteries have been widely investigated last decade (Larcher and Tarascon, 2015). Alternative anode active material using electrochemical deposition-dissolution process of less-noble metal is one strategy for the development of high-energy battery system (Lin et al, 2017). Among various choices of the less-noble metal anodes, magnesium is one of the potential candidates as the high-energy anode active material, because the volumetric capacity: 3,800 mAh cm−3 is 1.9 times higher than that of lithium metal, and no dendritic growth during the deposition process (Matsui, 2011). The organohaloaluminate electrolyte solutions, which are widely studied by Aurbach et al in early 2000s (e.g., Aurbach et al, 2000, 2003, 2007), Magnesium-Based Intermetallic Anode Active Materials show highly reversible deposition/dissolution of magnesium metal, since these electrolyte solutions contain halides: Cl− or Br−, the potential window of the organohaloaluminate electrolyte solutions is limited. A fluorinated alkokyborate-based electrolyte: magnesium hexafluoroisopropylaluminate (Mg[B(hfip)4]2) shows excellent reversibility without the corrosive properties
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