Electrolyte design for aqueous Zn batteries

Abstract

Polarity scales are often used as descriptors for selecting organic molecules for aqueous Zn battery (AZB) electrolytes. However, failure to accurately predict the solvation of Zn²⁺ raises questions about their applicability for designing high-performance AZB electrolytes. Here, Dimroth and Richardt’s Et(30) polarity scale is introduced as an effective guideline for screening organic molecules. A clear volcanic correlation is demonstrated between Et(30) and Zn Coulombic efficiency (CE). This challenges the common consensus in the aqueous electrolyte design formula, which typically uses highly polar organic molecules to improve Zn CE, and indicates that the roles of organic molecules beyond altering the Zn²⁺ solvation structure are critical for obtaining high AZB performances. Based on the Et(30) scale, the designed electrolyte achieves a high average Zn CE (99.8%), an exceptionally long cycle life (5,500 h), and a high specific energy (110 Wh kg⁻¹). Et(30) polarity scale offers general frameworks for selecting organic molecules in aqueous electrolytes.