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

Abstract

Magnesium metal batteries (MMBs) are considered as promising next-generation battery systems owing to their high theoretical capacity and elemental abundance of Mg. 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 based on conventional electrolytes to enhance the crystallographic orientation selectivity of Mg deposition and modulate the interfacial solvation structure of Mg²⁺. This additive enabled the customization of the vertical electrodeposition of Mg with a preferential orientation for (110) crystal planes. The dipole–dipole interaction between the solvent and BrFB induced a weakened shielding effect towards Mg²⁺ and enhanced the reaction kinetics at the electrolyte/electrode interface. The in situ construction of a Br/F hybrid interface during cycling facilitated the suppression of parasitic reactions and dendrite proliferation under extreme operating conditions. The symmetric cells exhibited plating/stripping cycling under an ultra-high areal capacity of 30 mA h cm⁻² with an exceptional Mg utilization rate of 89%, ultra-long cycling over 7000 h with a low overpotential of less than 190 mV, and stable cycling over 2800 h at a low temperature of −20 °C. The asymmetric cells exhibited a significantly enhanced average coulombic efficiency of 98.15% over 1800 cycles. The Mg||CuS full cell exhibited a high reversible capacity of approximately 200 mA h g⁻¹ and excellent rate performance. Thus, the synergistic customization of solvation structure, solid–electrolyte interface and preferred electrodeposition orientation offers a promising strategy for developing highly durable Mg metal anodes for practical MMBs.