Efficient Aqueous Static Zinc-Bromine Batteries Enabled by Hydrophobic Organic Bromide Design.

Aqueous static zinc-bromide batteries have emerged as promising candidates for large-scale energy storage owing to their intrinsic safety and low cost. However, practical application is hindered by the shuttle effect of polybromides, which leads to energy inefficiency and poor cycling stability. Herein, a self-capturing organic bromine compound is reported, 2,6-dimethyl-1-butylpyridinium bromide, developed via hydrophobic functionalization of the pyridine ring. These features collectively enable efficient polybromide capture and promote reversible solid-state complexation. When implemented in zinc-bromide batteries, the compound demonstrates exceptional electrochemical performance, retaining 81.94% of its initial capacity over 1500 h at 0.5 C and enabling 500 stable cycles at 2 C with a Coulombic efficiency of 99.46% and energy efficiency of 91.58%. The battery retains high performance even at elevated temperatures (60 °C). The pouch cell demonstrates a high energy density of 54.87 Wh kg-1 or 100.09 Wh L-1 with 96.59% Coulombic efficiency. These results highlight the potential of hydrophobic organic bromide in advancing zinc-bromide battery technologies toward scalable, durable, and high efficiency energy storage.