Passivation Layer Formation of Magnesium Metal Negative Electrodes for Rechargeable Magnesium Batteries

A comparative study for electrodeposited magnesium metal was conducted using an organohaloaluminate-based electrolyte solution and a conventional ionic electrolyte solution. The deposition/dissolution process of the magnesium metal in the ionic electrolyte solution shows high overpotential with low coulombic efficiency, compared with the organohaloaluminate-based electrolyte solution. The magnesium metal deposited in the ionic electrolyte solution shows porous morphology and poor crystallinity. An initial electrolytes decomposition process on Pt substrate was analyzed with in situ FTIR. The in situ FTIR spectra show passivation process of the electrode during the 1st cathodic scan due to the decomposition of the conventional ionic electrolyte solution. The surface layer on magnesium metal was characterized by using XPS. The XPS spectra for the magnesium metal immersed in the ionic electrolyte solution proved that a MgF2-based passivation layer corresponding to the decomposed TFSA anion is formed.