Building Organic–Inorganic Robust Interphases from Deep Eutectic Solution for Highly Stable Mg Metal Anode in Conventional Electrolyte

Abstract Magnesium metal batteries (MMBs) currently face challenges suffering from severe Mg metal passivation and extremely high overpotential in conventional electrolytes. Herein, a strategy of using a low‐cost deep eutectic solution (DES) is proposed to modify Mg anode with the monolithic and compact coating of a MgCl 2 ‐Al‐MgCl 2 sandwich structure, enabling the stable and reversible Mg plating–stripping behavior. An organic/nanocrystal hybrid interphase is in‐situ built through a facile Mg‐Al displacement reaction between aluminum‐chloro clusters and Mg in AlCl 3 /Et 3 NHCl solution, and it can effectively minimize the adverse interfacial passivation reaction and surface diffusion barrier, affording the high ion‐conduction and electronic insulation. This DES‐assisted method guarantees a highly reversible cycling of Mg metal anode (over 5000 h at 0.1 mA cm −2 and 400 h at 2.0 mAh cm −2 ) in Mg(TFSI) 2 /DME electrolyte with the improved interfacial kinetics and low overpotential. Even at a much higher current density of 1 mA cm −2 , the overpotential only undergoes a slight increase from 0.2 V (at 0.1 mA cm −2 ) to 0.23 V. The corresponding full cells with CuS and phenanthraquinone cathodes deliver satisfactory cyclic performance. The DES modification strategy provides a new solution to the design of robust and conductive solid electrolyte interphase for achieving high‐voltage and durable MMBs.