context: Implementability of Mg metal as an anode in magnesium-ion batteries (MIBs) mostly results from the dendrite-free nature of Mg during electrochemical plating/stripping, although it has been recently reported that the dendritic growth of Mg is dependent on the electrolyte nature and current densities. This feature provides potentially significant advantages to battery fabrication and/or electrochemical performance. For example, Mg metal delivers a higher volumetric capacity (3833 mA h cm−3) than either graphite (841 mA h cm−3) or Li metal (2047 mA h cm−3) in lithium-ion batteries, which enables cell designs that are more compact and flexible. The natural abundance of Mg (29k ppm in the Earth’s crust) is an additional benefit, in comparison with the limits of Li as a natural resource. The reversibility of Mg plating/stripping, however, is quite sensitive to the electrolyte system. The passivation of the Mg surface in conventional electrolytes restricts the versatility of utilizable electrolytes. To overcome this problem, various types of specially designed Mg-compatible electrolytes have been introduced during the past few decades: ‘all phenyl complex’ (APC); ‘magnesium aluminum chloride complex’ (MACC); [(DTBP)MgCl + MgCl2] (DTBP = 2,6-di-tert-butylphenolate); and [PhMgCl + MgCl2]. These electrolytes have shown reasonable levels of reversibility for Mg plating/stripping, but the relatively low anodic stability (≤ca. 3.0 V vs. Mg/Mg2+) and/or the difficulty in reaching high coulombic efficiencies remain problematic if MIBs are to move one step closer to commercialization.
answer: Mg metal