Solvation Regulation of Flame‐Retardant Bromine‐Based Electrolyte Enables Stable Cycling Dual‐Ion Battery

Dual-ion batteries (DIBs) have emerged as an attractive electrochemical energy storage technology owing to the distinctive advantages of cost-effectiveness, high operating voltage, and high power density. Nevertheless, conventional electrolytes face critical challenges including insufficient oxidation stability and severe flammability. Herein, a brominated electrolyte design for DIBs is proposed for the first time, and as an example of this strategy, ethyl acetate (EA) is selected for bromination. As a result, effectively suppressed electrolyte decomposition under high voltage, enhanced electrolyte/electrode compatibility by forming LiF/LiBr-rich interfaces, and anti-corrosive capability toward the aluminum current collector are simultaneously achieved with bromoethyl acetate (Br-EA) based electrolyte. Besides, compared to fluorine-based and chlorine-based electrolytes, bromine-based electrolyte demonstrates superior flame-retardancy. With the developed 6.0 m LiFSI Br-EA:DMC (1:1, v/v) electrolyte, the dual-graphite battery maintains 85.6% capacity retention after 1000 cycles, among the best reported results; the pouch cell employing this electrolyte retains 79.8% of initial discharge capacity over 500 cycles, validating its practical feasibility. This research work establishes bromination design as a groundbreaking paradigm for high-voltage and high-safety battery systems.