Anion-cation synergy enables reversible seven-electron redox chemistry for energetic aqueous zinc-iodine batteries

Abstract

Aqueous zinc-iodine batteries have drawn intensive attention from battery community due to the high theoretical capacity and low cost. However, the traditional two-electron-transfer and four-electron-transfer mechanisms suffer from low capacity and inferior stability due to the sluggish kinetics and low I^– utilization. Herein, we design a seven-electron-transfer Zn||I₂ battery via the anion-cation synergistic electrode reaction in layered BiI₃. The three-electron-transfer of Bi⁰/Bi³⁺, together with the four-electron-transfer of I^–/I⁺, endows Zn||BiI₃ battery with high capacity (∼370 mAh g^–1 at 1 A g^–1) and high energy density. The chemical confinement of I^– by Bi³⁺ and the effective conversion of I^– in BiI₃ eradicate side reactions and enable I^– with high utilization rate. Zn||BiI₃ battery delivers a good cycling stability (10,000 cycles) and a high coulombic efficiency. This work presents an anion-cation synergy method for stabilizing Zn||I₂ batteries and other conversion-type batteries such as Zn||Br₂, Li||I₂, and Li||Br₂.