A Water-in-Ester Electrolyte with Controllable Water Activity for Highly Reversible Zinc Anodes

Abstract

Rechargeable aqueous zinc batteries, featuring intrinsic safety, low cost and terrific recyclability, are an emerging and engaging technology potentially for stationary energy storage. However, this technology is blocked by the instability of zinc anode/electrolyte interface, due to the water-induced hydrogen evolution and dendrite growth. Herein, we formulate a water-in-ester electrolyte to effectively regulate the water activity by controlling the molar ratio of H2O to γ-valerolactone. The γ-valerolactone gets in on the solvation of Zn2+ ions, helping to exclude almost all bound water molecules from the solvation shell, and interacts with free water via forming intermolecular hydrogen bonds, thus completely confining water molecules in γ-valerolactone network. Thanks to the constrained H2O molecules and the reduced water activity, Zn anodes exhibit heighted anti-corrosion abilities in the water-in-ester electrolyte compared with the pure water electrolyte. The zinc deposition morphology evolves from hexagonal dendrites to tense particles, as the pure water electrolyte is transformed to the water-in-ester electrolyte. Water-in-ester electrolytes as well promise less hydrogen production, and eventually improve the average columbic efficiency and cycling stability of asymmetric Zn ‖ Ti cell from less than 85% and merely 10 cycles to 99.6% and over 500 cycles. The cycling lifespan of symmetric Zn ‖ Zn cell is extended to more than 1100 h at 1 mA cm-2 and 1 mAh cm-2 with the water-in-ester electrolyte, fourfold higher than that of the pure water electrolyte. Additionally, superior full cell performance is demonstrated for the newly formulated electrolyte. This work sheds light on the strong correlation between water activity and performance of zinc anodes and contributes to developing more stable aqueous zinc batteries by restricting water activity.