Homogeneous Complexation Strategy to Manage Bromine for High‐Capacity Zinc–Bromine Flow Battery
Qinghua Xiong, Mingbao Huang, Tianlu Ren, Shixi Wu, Wenfeng Wang, Zhipeng Xiang, Kai Wan, Zhiyong Fu, Zhenxing Liang
Abstract
Abstract Zinc–bromine flow batteries (ZBFBs) have received widespread attention as a transformative energy storage technology with a high theoretical energy density (430 Wh kg −1 ). However, its efficiency and stability have been long threatened as the positive active species of polybromide anions (Br 2 n +1 − ) are subject to severe crossover across the membrane at a high concentration. Herein, a novel highly hydrophilic complexing agent, N‐methyl‐N, N‐bis(2‐hydroxyethyl)‐1‐propanaminium bromide (PMDA), is developed to effectively manage bromine in a homogeneous posolyte, which realizes a low bromine crossover at a high operating concentration in ZBFBs. Both theoretical and experimental results suggest that the PMDA interacts with Br 2 n +1 − and forms a larger‐size complex PMDABr 2 n +1 . When adding 0.40 m PMDA, the bromine stays homogeneous at a high concentration up to 1.20 m , and its permeability is remarkably decreased by 74%. For demonstration, the ZBFB achieves a operating capacity record of 57.2 Ah L −1 in a homogeneous bromine posolyte with a high Coulombic efficiency of ≈90.0% and superior cycling stability (capacity retention rate of 100.0% per cycle). This work provides one innovative bromine management strategy to realize a high capacity and superior stability in ZBFBs.