Grid-scale corrosion-free Zn/Br flow batteries enabled by a multi-electron transfer reaction

Flow batteries are promising for renewable energy storage due to their safety and scalability. Zinc/bromine flow batteries (Zn/Br) are popular due to their high energy densities and inexpensive electrolytes. However, they have a poor service life and lead to environmental harm as a result of the generated corrosive and volatile Br 2 . Here we introduce a Br 2 scavenger to the catholyte, reducing the Br 2 concentration to an acceptable level (~7 mM). The scavenger, sodium sulfamate (SANa), reacts rapidly with Br 2 to form a mild product, N -bromo sodium sulfamate (Br-SANa; Br + ). Additionally, the two-electron transfer reaction of Br-SANa/Br − (Br + /Br − ) increases the energy density. We have developed a Zn/Br flow battery, paired with a Zn anode, that outperforms traditional Zn/Br flow batteries in energy density (152 Wh l −1 versus 90 Wh l −1 ) and cycle life (>600 versus 30 cycles), using a sulfonated polyetheretherketone membrane. We assembled a 5-kW stack that operated stably for over 700 cycles (~1,400 h). Using this reaction, we have built a large-scale battery system.