A bromine-rich artificial interphase to regulate interfacial kinetics in boron-centered electrolytes for magnesium metal batteries

Abstract

Rechargeable magnesium batteries (RMBs) have emerged as promising next-generation energy storage systems owing to their high volumetric energy density and inherent safety. However, the passivation of magnesium (Mg) anodes and irregular Mg deposition in conventional electrolytes severely limit their reversibility and long-term cycling stability. Although advanced boron-centered electrolytes enable reversible Mg plating/stripping without anode passivation, interfacial challenges and irregular Mg deposition still persist, compromising cycling stability and coulombic efficiency (CE). Here, we design a bromine-rich artificial interphase on Mg anode (Br-Mg) that effectively mitigates interfacial challenges and regulates deposition homogeneity. The Br-Mg anode demonstrated an extended cycling life of 1610 hours in symmetric cell, while maintaining a low voltage hysteresis of only ±68 mV, a substantial improvement from 796 hours and ±145 mV for bare Mg. Furthermore, the CE of Mg plating/stripping process measured in asymmetric cell increased from 96.47% with bare Mg to 99.50% with the Br-Mg anode, with extended cycling life from 380 cycles to 1630 cycles. The superior electrochemical performance is attributed to favorable interfacial kinetics imparted by the Br-rich interphase, which ensures high ionic mobility and suppresses electrolyte-induced degradation. In full-cell configuration with Mo6S8 cathode, the Br-Mg anode delivered stable cycling and high capacity. This study provides a strategic design concept for creating efficient artificial interphases on Mg anodes to improve reversibility and CE in boron-centered Mg electrolytes.