"Zn-Iodine" Co-Regulation Induced by Trifunctional Zn2+-Exchanged Electrolyte Additives for High-Areal-Capacity and Robust Zn-I2 Batteries.

Abstract

Aqueous Zn-I2 batteries featuring high safety and low cost attract considerable attention for grid-scale energy storage. However, the challenges of Zn dendrite growth, hydrogen evolution reaction, and polyiodide shuttling severely impede their practical application. This study introduces Zn2+-exchanged vermiculite nanosheets (ZVN) as a multifunctional electrolyte additive to optimize Zn2+ solvation structure, facilitating hydrated Zn ion de-solvation via the strong electron affinity of ZVN. Moreover, the in situ formed protective ZVN layer on Zn anode maintains superior ionic conductivity for Zn2+ transportation, enabling highly stable and dendrite-free Zn deposition. This dual mechanism enables a dendrite-free Zn anode with 99.82% Coulombic efficiency over 1 700 cycles in Zn//Cu cells. Simultaneously, the excellent iodine species trapping ability of ZVN effectively inhibits the polyiodide shuttling for improved iodine conversion efficiency. Therefore, the assembled Zn-I2 battery based on polyaniline/I- cathode exhibits a high areal capacity of 1.05 mAh cm-2 and ultra-long lifespan over 18 000 cycles. This study provides an efficient electrolyte additive with a "Zn-iodine" synergistic effect for advanced Zn-I2 batteries.