Aqueous Zinc‐Bromine Battery with Highly Reversible Bromine Conversion Chemistry

• Published in: Angewandte Chemie International Edition Vol. 64; no. 20; pp. e202502386 - n/a
• Main Authors: Zhao, Xun, Hao, Junnan, Chen, Qianru, Zhang, Shao‐Jian, Wu, Han, Mao, Lei, Qiao, Shi‐Zhang
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 12.05.2025
• Edition: International ed. in English
• Subjects: Aqueous electrolytes; Bromine; Cathodes; Charge density; Discharge; electrolyte screen; Electrolytes; Electrolytic cells; KBr cathode; polybromide sequestration; static Zn−Br battery; suppressed shuttle; Zinc; Zinc salts; Zinc sulfate; polybromide sequestration; KBr cathode; suppressed shuttle; static Zn−Br battery; electrolyte screen
• DOI: 10.1002/anie.202502386
• ISSN: 1433-7851; 1521-3773

Br2/Br− conversion reaction with a high operating potential (1.85 V vs. Zn2+/Zn) is promising for designing high‐energy cathodes in aqueous Zn batteries. However, the ultrahigh solubility of polybromides causes significant shuttle effects, capacity deterioration, and self‐discharge, rendering the study of static zinc‐bromine batteries still in its infancy. Here, various aqueous zinc salt electrolytes are first screened, showing that, compared to other salts, ZnSO4 is more suitable for Br‐based cathodes benefiting from its higher negative charge density and lower cost. Nevertheless, the significant shuttle effect of polybromides remains in such an electrolyte. We further develop a targeted sequestration strategy to fundamentally confine polybromide migration from KBr cathode into electrolyte. In high‐mass‐loading (22 mgKBr cm−2) pouch cells, the average Coulombic efficiency enhances from 92.3 % to 99.8 %, and self‐discharge performance dramatically improves from 17.4 % capacity retention to 85.2 % after 72 h of resting, indicating the effectiveness of our strategy in confining the shuttle effects. Furthermore, an Ah‐scale pouch cell delivers an average Coulombic efficiency of 99.88 % and a zinc utilization of 22 % at a high rate of 3 C. Our findings also pave the way for the design of advanced Br‐based cathodes. ZnSO4 solution is initially screened as the electrolyte for bromide cathodes. Subsequently, a targeted sequestration strategy is proposed to modify KBr cathode, achieving high‐reversibility bromine conversion chemistry. In situ Raman spectra reveal a Br3−/Br−‐dominated conversion mechanism. A large‐capacity Zn−Br pouch cell exhibits a high capacity retention of 98.46 % and an average Coulombic efficiency of 99.92 % after 775 cycles at 3 C.