A Quasi‐Solid Ionic Liquid‐Polymer Hybrid Electrolyte for Shuttle‐Free and Dendrite‐Free Aqueous Zinc─Bromine Batteries

ABSTRACT Aqueous static zinc─bromine (Zn─Br) batteries hold promise for grid‐scale energy storage but still suffer from severe polybromide shuttling and poor Zn reversibility. Here, we develop a quasi‐solid ionic liquid‐polymer hybrid electrolyte by integrating a sulfonated polymer matrix with anchored 1‐butyl‐3‐methylimidazolium (BMI ⁺ ) cations. The fixed −SO ₃ ⁻ groups construct highly Zn ²⁺ selective conduction channels, while BMI ⁺ forms strong electrostatic interactions with the polymer, generating immobilized ionic‐liquid domains that effectively capture polybromides. This hybrid design transforms BMI ⁺ from a soluble additive into a structural component of the quasi‐solid framework, thereby enabling simultaneous dendrite‐free Zn plating/stripping and shuttle suppression. With this multifunctional regulation, the Zn─Br batteries achieve a high initial capacity of 162.7 mAh g ⁻¹ , a discharge plateau of ∼1.78 V, and 25 000‐cycle durability at 20 C. Moreover, the pouch cell with high‐loading Br cathodes (∼14 mg _KBr cm ⁻² ) retains 90.9% capacity after 1500 cycles. This work demonstrates that quasi‐solid ionic liquid‐polymer hybrid electrolytes can deliver shuttle‐free, long‐lasting Zn─Br batteries, pointing to a promising pathway for scalable and reliable aqueous energy storage.