Interrupting the Hydroxide Enrichment-Induced Electrode Degradation Loop for Achieving Stable Aqueous Zn-I₂ Batteries

Severe adverse reactions, including hydrogen evolution reaction (HER) and polyiodide shuttle, lead to short lifetimes of rechargeable aqueous zinc-iodine (Zn-I₂) batteries and have aroused widespread attention. However, few studies have specifically investigated the impact of hydroxide ion (OH^-) disturbance generated by side reactions on the Zn anode and I₂ cathode in aqueous electrolytes. Herein, a facile electrolyte additive strategy was introduced to break the OH^- enrichment-induced bidirectional electrode degradation loop toward achieving stable Zn-I₂ cells. Particularly, the bidirectional additive restricts the crossover of OH^-, suppressing the iodine hydrolysis reaction-induced polyiodide formation and capturing polyiodides to prevent shuttling. It also preferentially interacts with Zn, simultaneously reconstructing the solvation shell and promoting the formation of a hybrid ZnS-rich solid electrolyte interface (SEI) to improve Zn kinetics and inhibit HER. Therefore, a stable cycling of Zn//Zn cells can be sustained for 1700 and 400 h in acidic and alkaline electrolytes, respectively. Impressively, the Zn-I₂ cell achieved a cycle life of 9000 cycles at a high mass loading of 12 mg cm^-2. The concept of bi-directional synergetic regulation for accounting for the aqueous environment is expected to provide a new approach for highly stable aqueous Zn-I₂ batteries.