An Inter‐Locking Quasi‐Solid Cathode for Zinc‐Bromine Batteries with Stable 32000 Cycles

Abstract Zinc‐bromine static batteries employing solid bromine cathodes present compelling advantages of low‐cost, high‐safety, and extended‐lifespan for large‐scale energy storage applications. However, solid‐state bromine cathodes suffer from polybromide‐induced shuttle effects and substantial volume variations, leading to poor reversibility and severe self‐discharge. Herein, an inter‐locking, quasi‐solid bromine cathode enabling energetic static zinc‐bromine batteries are developed. Theoretical calculation and characterizations confirm that polyacrylamide (PAM) effectively encapsulates tribromide molecules within the charged bromine cathode, suppressing bromine dissolution and mitigating self‐discharge. Meanwhile, its flexibility accommodates volume changes and maintains conductive integrity. The resultant zinc‐bromine battery achieves ≈32000 cycles at 1 mAh cm −2 , with an ultralow decay rate of 0.00016% per cycle. Meanwhile, it delivers scalable areal capacity up to 50 mAh cm −2 . Pouch cell with 200 mAh demonstrates remarkable stability of 3500 cycles, while displays capacity retention of ≈93% after 48 h resting. The 1.5 Ah pouch cell delivers a practical energy density of 70 Wh kg −1 based on the total mass of pouch cell, while its modular integration (≈18 Wh) enables storage of hybrid energy harvesting from solar and wind sources, demonstrating versatile applicability in multi‐scenario energy systems. This strategy establishes a viable pathway for developing practical zinc‐bromine batteries toward grid‐scale energy storage applications.