Reviving Multivalent‐Metal Anodes in Simple Salt Electrolytes via Component Modifier Design

Abstract Using combinatory electrolyte blends represents an imperative avenue to achieve good magnesium (Mg)‐metal anode compatibility and commercial feasibility in fields of promising rechargeable Mg batteries. However, fundamental challenges of how to manipulate component modifier reactivity on molecule level still remain to be solved. Here, molecular structure design concepts towards seeking bromophenyl complex‐based component modifiers has been proposed according to implications of electron‐donating and/or electron‐withdrawing substituents on Br−C bond dissociation reactivity. Exceptional Mg electro‐plating/stripping properties (a stable cycle life of 250 days in Mg//Cu asymmetric cells) have been firstly achieved in a simple salt electrolyte with 1‐(3‐bromophenyl)‐N,N‐dimethylmethanamine (BPDMA) as optimal component modifier. Comprehensive analyses disclose the unique electrochemically‐active Br‐containing ion‐pairs formation, such as [(Mg 2+ ) 2 (TFSI − )Br − ] 2+ and [(Mg 2+ ) 2 (TFSI − )(Br − )(G2) 2 ] 2+ , which results in the much thinner Br − containing and organic–inorganic mixed interphases on Mg‐metal anodes. Furthermore, conventional MgSO 4 ‐based electrolytes and even calcium (Ca)‐ion electrolytes can also be revived by similar strategy, demonstrating its generality and superiority.