Choline Iodide-Mediated Sulfur Conversion and Zinc Plating/Stripping Chemistry in Aqueous Zn–S Batteries

Abstract

Aqueous Zn–S batteries are promising candidates for future energy storage due to their intrinsic safety, environmental friendliness, and low cost. However, their practical application is hindered by sluggish sulfur redox kinetics and rapid zinc anode degradation. Here, we introduce choline iodide (ChI) as a multifunctional electrolyte additive that enables bidirectional catalysis of sulfur conversion and simultaneous protection of the zinc anode. During discharge, Ch⁺ promotes the formation of soluble polysulfide intermediates, which rapidly combine with Zn²⁺ to form ZnS via a solid–liquid–solid pathway, accelerating reaction kinetics. During charge, iodine species catalyze the conversion of ZnS back to sulfur. Moreover, Ch⁺ adsorbs on the zinc anode, suppressing dendrite growth and the hydrogen evolution reaction. Importantly, Ch⁺ also inhibits polyiodide shuttling at high iodine concentrations, maximizing catalytic efficiency. Coupled with a CoNC solid-phase catalyst, the Zn–S cell achieves a record-low polarization of 0.26 V at 0.1 C, delivers 780 mAh g⁻¹ at 10 C, and maintains 380 mAh g⁻¹ after 5500 cycles.