A reversible Br2/Br− redox couple in the aqueous phase as a high-performance catholyte for alkali-ion batteries

An aqueous catholyte based on the sole bromine/bromide redox couple shows an operating potential of ∼4 V, a reversible capacity of 290 mA h g⁻¹, and a specific power density approaching 1000 W kg⁻¹, making it a potential candidate for sustainable electrical energy storage.