Abstract:

Rechargeable Mg batteries are a promising post-Li-ion battery technology, but its development has been critically hampered by the passivating nature of Mg, particularly in aqueous solutions. Due to a quick dismissal of its reversibility, the use of Mg anodes in aqueous electrolytes has been unfortunately overlooked, and most researchers focus on non-aqueous systems instead. In this seminar, a reversible, aqueous Mg battery mechanism will be introduced. Using a MgCl2 water-in-salt (WIS) electrolyte, the impermeable passivation film on Mg could be converted to a conductive metallic oxide complex, facilitated by Cl- regulation and the suppression of hydrogen evolution reaction. When coupled with copper hexacyanoferrate as the cathode, the full battery exhibits an impressive voltage plateau of 2.4-2.0 V, and excellent stability of over 700 cycles with a Coulombic efficiency of up to 99% at 0.5 A g-1. The interfacial chemistry of Mg in the MgCl2 WIS electrolyte raises the once dismissed possibility of reversible Mg dissolution and deposition in aqueous solutions.