Synergistic Interface-Bulk Regulation of Biopolymer Electrolytes for Advanced Zn-Iodine Batteries With Four-Electron...

Aqueous zinc||iodine batteries (AZIBs), which rely on the efficient I^-/I⁰/I⁺ conversion chemistry, offer high theoretical energy density. However, their practical application is hindered by the polyiodide (I₃ ^- and I₅ ^-) shuttle effect, I⁺ hydrolysis at the iodine cathode, and poor reversibility at the Zn anode. To address these challenges, we propose a synergistic interface-bulk regulation strategy using oppositely charged biopolymers. A negatively charged sodium alginate (SA) hydrogel serves as the bulk electrolyte matrix, while positively charged quaternized chitosan (qChi) is introduced as a functional additive. In this system, the abundant carboxyl groups along the SA chains not only facilitate uniform Zn²⁺ deposition but also electrostatically repel polyiodides. Meanwhile, the amine and quaternary ammonium groups along the qChi chains can strongly bind polyiodides and ICl₂ ^- species via ionic interactions, thereby effectively suppressing the shuttle effect and stabilizing I⁺ against hydrolysis. Consequently, highly durable two-electron and four-electron AZIBs are achieved, delivering remarkable cycling lifespans of 20 000 and 10 000 cycles with ultralow capacity decay rates of 0.00054% per cycle and 0.17% per hundred cycles, respectively. Notably, the AZIBs also maintain excellent performance in a natural seawater-based electrolyte, highlighting their potential as sustainable and high-performance energy storage systems.