Establishing High-Performance Quasi-Solid Zn/I2 Batteries with Alginate-Based Hydrogel Electrolytes.

Abstract

Zinc-iodine (Zn/I2) batteries are recognized as a kind of leading candidate for large-scale energy storage systems, owing to the high-capacity dissolution-deposition reactions on both electrodes. Nevertheless, the lifespan of Zn/I2 batteries is severely limited by the uncontrolled shuttling of triiodide ions (I3-) and unfavorable side reactions on Zn anodes. Herein, an alginate-based polyanionic hydrogel electrolyte is designed and synthesized by ion exchange and Zn2+-induced cross-linking. The immobile, negatively charged polyanionic chains on the hydrogel skeleton effectively block I3- from shuttling, while simultaneously transporting cations that are indispensable for battery chemistry. Moreover, this hydrogel can also enhance the cycling durability of Zn anodes by alleviating Zn s dendritic growth and corrosion reactions, due to the homogenized Zn2+ flux and reduced interfacial contact between free water and metallic Zn. Consequently, this alginate-based hydrogel electrolyte enables stable Zn plating/stripping for over 600 h at 2 mA cm-2 and 2 mAh cm-2 (corresponding to 10% depth of discharge). Serving as an electrolyte for Zn/I2 full batteries, this hydrogel helps the battery to achieve a high capacity of 183.4 mAh g-1 (capacity retention = 97.6%) after even 200 cycles at 0.2 A g-1, 77.4% higher than that of the traditional ZnSO4 aqueous counterpart (residual capacity = 41.5 mAh g-1). This work indicates the promising potential of electrolyte design on the performance improvement of aqueous Zn/I2 batteries.