A polybromide confiner with selective bromide conduction for high performance aqueous zinc-bromine batteries

Aqueous zinc-bromine batteries are promising energy storage systems. The non-flow setup largely reduces the cost, and the application of Br− containing electrolytes transform the volatile charged product Br2 to polybromide. However, the shuttling of soluble polybromide species causes poor coulombic efficiency and corrosion of the negative electrode. Herein, we design a composite positive electrode of polybromide confiner and conductive agent for non-flow zinc-bromine batteries. The (2-bromoethyl) trimethylammonium bromide and hexyl bromide are grafted as the side chains of poly(biphenyl pyridine). The obtained PBP-BTAB-HB polymer provides selective bromide conduction whereas hinders polybromide diffusion through steric hindrance. It forms uniform layer on the Super P carbon particles, resulting in the composite electrode with facile electron and bromide transports as well as polybromide restriction. In the aqueous zinc-bromine battery, the positive electrode presents high coulombic, voltage and energy efficiencies of 92%, 81% and 74%, respectively, at 8 mA cm−2 with 2 mAh cm−2 charge capacity. Stable cycling is achieved for 1200 cycles with 99.8% capacity retention. The high electrochemical performance is preserved at a low temperature of 0 °C. A pouch cell is also demonstrated, delivering 18 mAh capacity at 100 mA. Our work offers a promising path for high-performance zinc-bromine batteries.