Hydrophilic modification of polyethylene membrane for long life zinc-bromide flow batteries

Zinc-bromine flow batteries are considered as one of the most promising energy storage devices with high energy density and low production price. However, its practical application is hampered by the short cycle life, which is mainly due to the uneven zinc deposition and the shuttle effect of bromide ions. Modification of membranes, an important part of zinc-bromine flow batteries, is a common approach to address these issues. In this study, inspired by the adhesion mechanism of filament proteins secreted by marine mussels, we propose a novel method for modifying polyethylene membranes with polydopamine. The self-polymerization of dopamine on a polyethylene membrane surface is simple and mild compared to traditional methods. This dopamine-based modification enhances the hydrophilicity of polyethylene membrane, improves ion transport, and reduces the pore size of the membranes, effectively blocking bromine ion shuttling. Additionally, polydopamine modification promotes uniform zinc deposition, further improving the battery performance. Consequently, the resulting PDA@PE-24 membrane demonstrates a significant improvement in both voltage and energy efficiencies, reaching 83.5% and 79.7%, respectively, under 20 mA·cm⁻², compared to the 80.3% and 76.5% voltage and energy efficiencies, respectively, for unmodified polyethylene membranes. Furthermore, the cycle life of a single cell increased 4-fold, operating continuously for more than 2000 h. (Figure presented.)