Highly Reversible Aqueous Zinc Batteries enabled by Zincophilic-Zincophobic Interfacial Layers and Interrupted Hydrogen-Bond Electrolytes

Abstract

Aqueous Zn batteries promise high energy density but suffer from Zn dendritic growth and poor low-temperature performance. Here, we overcome both challenges by using an eutectic 7.6 m ZnCl₂ aqueous electrolyte with 0.05 m SnCl₂ additive, which in situ forms a zincophilic/zincophobic Sn/Zn₅ (OH)₈ Cl₂ ⋅H₂ O bilayer interphase and enables low temperature operation. Zincophilic Sn decreases Zn plating/stripping overpotential and promotes uniform Zn plating, while zincophobic Zn₅ (OH)₈ Cl₂ ⋅H₂ O top-layer suppresses Zn dendrite growth. The eutectic electrolyte has a high ionic conductivity of ≈0.8 mS cm^-1 even at -70 °C due to the distortion of hydrogen bond network by solvated Zn²⁺ and Cl^- . The eutectic electrolyte enables Zn∥Ti half-cell a high Coulombic efficiency (CE) of >99.7 % for 200 cycles and Zn∥Zn cell steady charge/discharge for 500 h with a low overpotential of 8 mV at 3 mA cm^-2 . Practically, Zn∥VOPO₄ batteries maintain >95 % capacity with a CE of >99.9 % for 200 cycles at -50 °C, and retain ≈30 % capacity at -70 °C of that at 20 °C.

Keywords: aqueous zinc batteries; hydrogen bonds; low temperature; salt precipitation; zincophilic-zincophobic interfacial bilayer.