Tailoring a Hybrid Functional Layer for Mg Metal Anodes in Conventional Electrolytes with a Low Overpotential

The development of high-voltage Mg metal batteries is hampered by the incompatibility between a Mg metal anode and conventional electrolyte, leading to a high overpotential for Mg plating/stripping processes. In this work, we tailored a hybrid functional layer consisting of Bi/MgCl₂/polytetrahydrofuran (PTHF) by an in situ THF polyreaction during the reaction of the Mg anode with BiCl₃ solution. The introduction of PTHF inhibits the growth of Bi particles and fills the layer interstice with MgCl₂-containing PTHF, improving the structural integrity of the functional layer and insulation between the electrolyte and Mg anode. As a result, compared to a simply modified Bi/MgCl₂ layer, the Bi/MgCl₂/PTHF functional layer exhibits a lower polarization voltage of 0.25 V and longer cycling life of more than 2000 h at 0.1 mA cm^-2. Mechanism analysis shows that Mg is plated on the surface of Bi particles within the layer. The Mo₆S₈/Mg full battery with the hybrid functional layer achieved a low voltage hysteresis of ∼0.25 V and long cycling life over 500 cycles at 50 mA g^-1. This work provides a facile and effective hybrid functional layer strategy to realize Mg metal batteries in conventional electrolytes.