Interface solvation regulation stabilizing the Zn metal anode in aqueous Zn batteries

Abstract

The Zn metal anode experiences dendritic growth and side reactions in aqueous zinc batteries. The regulation of the interface environment would provide efficient modification without largely affecting the aqueous nature of bulk electrolytes. Herein, we show that the ethylene carbonate (EC) additive is able to adsorb on the Zn surface from the ZnSO₄ electrolyte. Together with the higher dielectric constant of EC than water, Zn²⁺ preferentially forms EC-rich solvation structures at the interface even with a low overall EC content of 4%. An inorganic–organic solid-electrolyte interface (SEI) is also generated. Thanks to the increased energy levels of the lowest unoccupied molecular orbital of EC-rich solvation structures and the stable SEI, side reactions are suppressed and the Zn²⁺ transference number increases to allow uniform Zn growth. As a result, the cycle life of Zn stripping/plating in symmetric Zn cells extends from 108 h to 1800 h after the addition of 4% EC. Stable cycling for 180 h is realized with 35% depth of discharge in the 4% EC electrolyte, superior to the initial cell failure with EC-free electrolyte. The capacity retention of the Zn//V₆O₁₃·H₂O full cell with N/P = 1.3 also increases from 51.1% to 80.5% after 500 cycles with the help of EC.