Optimizing Bromine Complexation and Kinetics: a Bisimidazole Strategy for High-Performance Zn-Br Static Batteries.

Zinc-bromine (Zn-Br) static batteries are promising for large-scale energy storage, yet the practical application is hindered by the long-standing trade-off about bromine complexing agents (BCAs) between bromine complexation strength and redox kinetics. Herein, we report a rationally designed bisimidazolium salt, 1,4-bis(3-methylimidazolium-1-yl) butane dibromide ([bMImB]Br₂), which features a symmetric molecular structure that reconciles this contradiction. [bMImB]Br₂ demonstrates strong bromine affinity, stemming from its high atomic charge of N+ and low solubility-properties comparable to those of tetraalkyl-quaternary ammonium salts. Simultaneously, it retains low steric hindrance typical of monoimidazole compounds, thereby enabling fast electrode kinetics. As a result, Zn-Br batteries incorporating [bMImB]Br₂ deliver a high specific energy of 116 Wh·kg⁻¹, alongside an average coulombic efficiency (CE) of 99.22% and energy efficiency (EE) of 89.35% at 10 mAh·cm⁻2 (0.5 C) for over 150 cycles. Furthermore, the flexible pouch cell maintains a discharge capacity of 110 mAh and 99.7% CE over 100 cycles, even under mechanical deformation. This work offers a generalizable molecular design strategy for developing next-generation BCAs in halogen-based energy storage systems.