Hydrated eutectic electrolyte enabling stable low-temperature zinc metal batteries with a tuned inner Helmholtz plane and a solid electrolyte interface

Abstract

Aqueous zinc metal batteries (ZMBs) are promising for grid-scale energy storage, but their practical application is hindered by limited cycling life and inferior low-temperature performance, primarily due to Zn dendrite growth and parasitic reactions at the electrolyte-electrode interface. To address these challenges, we develop a new and cheap hydrated eutectic electrolyte (HEE) composed of ZnCl₂, choline chloride (ChCl), and H₂O, which can fundamentally tune desirable interface chemistries for dendrite-free and low-temperature ZMBs. The optimized HEE with a solvation structure of ZnCl₃(ChCl)(H₂O)₂ shows a high conductivity of 15.98 mS cm⁻¹ and excellent freeze resistance below −40 °C. It has been found that hydrogen bonding between ChCl and H₂O effectively reduces water activity, while preferential adsorption of ChCl molecules at the inner Helmholtz plane promotes the formation of a protective solid electrolyte interphase (SEI) on Zn metal anodes, which greatly suppresses the dendrites and side reactions. Therefore, the HEE endows the as-fabricated Zn//Zn symmetric cells and Zn//polyaniline full batteries with superior electrochemical performance at −40 °C, such as a long cycling life of 870 h at 1 mA cm⁻² and 1 mAh cm⁻² and a high capacity of 75 mAh g⁻¹ at 0.3 A g⁻¹. The HEE reported here may pave a new way to construct high-performance ZMBs for specific low-temperature application scenarios.