The selection of viable conventional magnesium salts in electrolyte solutions for Mg secondary batteries is very limited. Reversible magnesium deposition was demonstrated with only MgTFSI2, in ethereal solutions. A recent report has suggested that Mg can be reversibly deposited from a solution of Mg(PF6)2 in tetrahydrofuran and acetonitrile. In this paper, we dispute that claim and show that PF6- anions passivate Mg anodes and completely inhibit any Mg deposition/dissolution process. We show that addition of chlorides suppresses the passivation phenomena and allows reversible Mg deposition/dissolution processes to commence. The Mg deposits have been examined via elemental analysis, scanning electron microscopy, and X-ray diffraction measurements, depicting a highly oriented, preferential Mg growth. This study evaluates the feasibility of employing PF6-based electrolytes for Mg batteries and exemplifies the aptitude of chlorides for suppressing passivation phenomena.
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