Functional group differentiation of isomeric solvents enables distinct zinc anode chemistry

Abstract

Electrolytes hold the key to realizing reliable zinc (Zn) anodes. Divergent organic molecules have been proven effective in stabilizing Zn anodes; however, irrational comparisons exist due to the uncontrolled molecular weights and functional group amounts. In this work, two “isomeric molecules”: 1,2-dimethoxyethane (DME) and 1-methoxy-2-propanol (PM), with identical molecular weights but different functional groups, have been studied as co-solvents in electrolytes, which have delivered distinct electrochemical performance. Experimental and simulative study indicates the dipole moment induced by the hydroxyl groups in PM (higher molecular polarity than ether groups in DME) reconstructs the space charge region, enhances the concentration of Zn2+ in the vicinity of Zn anodes, and in-situ derives different solid electrolyte interphase (SEI) models and electrode–electrolyte interfaces, resulting in exceptional cycling stability. Remarkably, the Zn||Cu cell with PM worked over 2000 cycles with high Coulombic efficiency (CE) of 99.7%. The Zn||Zn symmetric cell cycled over 2000 h at 1 mA·cm−2, and showed excellent stability at an ultrahigh current density of 10 mA·cm−2 and capacity of 20 mAh·cm−2 over 200 h (depth of discharge, DOD of 70%). The Zn||sodium vanadate pouch cell with a high mass loading of 6.3 mg·cm−2 and a high capacity of 24 mAh demonstrates superior cyclability after 570 h. This work can be a good starting point to provide reliable guidance on electrolyte design for practical aqueous Zn batteries.

Keywords

• functional group
• isomeric solvents
• zinc anode
• solid electrolyte interphase (sei) model