Customizing vertical electrodeposition orientation and interfacial solvation to enable magnesium metal anodes with ultrahigh areal capacity

Abstract

Magnesium metal batteries (MMBs) are considered as a promising next-generation battery system due to the high theoretical capacity and element abundance of Mg anode. However, the potential interfacial passivation, sluggish desolvation kinetics and dendrite formation severely constrain the cycling stability of MMBs. In this work, we developed 3-bromofluorobenzene (BrFB) as a facet-termination additive in conventional electrolyte to construct highly crystallographic-oriented electrodeposition and modulate interfacial solvation structure of Mg2+. This additive enables to customize the vertical electrodeposition of Mg with preferential orientation of (110) crystal planes. The dipole-dipole interaction between solvent and BrFB induces the weakened shielding effect towards Mg2+ and enhances the reaction kinetics at electrolyte/electrode interface. The in-situ construction of Br/F hybrid interface during cycling facilitates the suppression of parasitic reaction and dendrite proliferation under extreme operating condition. The symmetric cells exhibit the plating/stripping cycling under ultra-high areal capacity of 30 mAh cm-2 with exceptional Mg utilization rate of 89%, ultra-long cycling over 7000 h with a low overpotential less than 190 mV, and stable cycling over 2800 h at a low temperature of -20 °C. The asymmetric cells enable the significantly enhanced average coulombic efficiency of 98.15% over 1800 cycles. The Mg||CuS full cell exhibits a high reversible capacity around 200 mAh g-1 and excellent rate performance. The synergistic customization of solvation structure, solid electrolyte interphase and preferred electrodeposition orientation offers a promising strategy for developing highly durable Mg metal anodes for practical MMBs.