Synchronous regulation on solvation structure and interface engineering to enable reversible magnesium metal batteries

Magnesium (Mg) metal anodes are highly regarded as one of ideal substitutes for lithium (Li) metal anodes owing to their exceptional volumetric capacity, remarkable safety property, and abundant crustal reserves. However, the development of Mg batteries is severely impeded by the limited availability of electrolyte types, particularly non-nucleophilic ones. Mg(TFSI)2-based electrolyte is a recently discovered type of electrolyte which is non-nucleophilic, easily prepared, and highly stable. Nevertheless, due to its challenging de-solvation process and unexpected passivation interlayers, it is not performing as well electrochemically and requires effective modification. Here, organic amine dihydrochlorides (NCxN·2HCl) are selected as additives to Mg(TFSI)2-based electrolytes to regulate solvation structure and electrode interlayer synchronously. It helps rearrange the solvation sheath of Mg2+ and forms a Mg2+-permeable solid electrolyte interphase (SEI) on the surface of anode, facilitating the kinetic. Amine cations could also guide uniform Mg2+ deposition through electrostatic shielding effects. After experiments and simulations, ethylenediamine dihydrochloride (NCCN·2HCl) stands out, contributing to a significantly reduced overpotential (< 0.2 V), realizing about 100% coulombic efficiency and stable long-term full cell cycling for an impressive 2400 cycles.