An aqueous Zn||Br₂ battery by electrolyte activating the positive charge of cyanidin additive to resolve challenges of both anode and cathode

Aqueous Zn||Br₂ batteries are deemed as highly promising candidates for high-energy storage due to their low cost, inherent safety, and high theoretical energy density. However, their practical applications are hindered by the poor reversibility of the Zn anode and severe dissolution of the Br₂ cathode. In this study, the cyanidin additive—characterized by a cationic property activated through the acidic nature of the ZnSO₄ electrolyte—simultaneously addresses challenges at both electrodes without exogenous ions. The −OH groups of cyanidin can bond with free H₂O molecules to suppress the hydrogen evolution reaction, and cyanidin can form an electrostatic protective layer on the Zn surface to promote the reversibility of the Zn anode. Simultaneously, cyanidin exhibits strong affinity for bromine species and accelerates their redox kinetics in the Br₂ cathode. As a result, the Zn||Br₂ coin cell achieves a discharge capacity of 225.5 mAh g^–1 with 99.2 % Coulombic efficiency after 20,000 cycles at 5 A g^–1, and retains 180 mAh g^–1 even at 30 A g^–1. Furthermore, the Zn||Br₂ pouch cell demonstrates stable cycling over 1400 cycles at 5 A g^–1. This work provides a new avenue for simultaneously addressing challenges at both electrodes in aqueous Zn||Br₂ batteries and promotes the development of advanced high-performance metal||halogen or metal||chalcogen batteries.