Freezing of Aqueous Electrolytes in Zinc-Air Batteries: Effect of Composition and Nanoscale Confinement

Abstract

Zinc-air batteries, which typically employ aqueous electrolytes, have attracted much attention owing to their high energy density, low cost, and environmental friendliness. While the zinc-air battery is a promising solution for energy grid applications, freezing of the electrolyte is an important problem for operation in cold climates. The freezing point of the electrolyte can be affected not only by chemical composition but also by micro/nanoscale confinement in porous electrodes or separators, and this is the focus of our work. First, we find osmotic virial coefficients by fitting experimental freezing point data for various electrolytes that are used in zinc-air batteries. Second, we show how additives that improve the performance of the batteries may also lower the freezing point of the electrolyte system. Third, we show how the nanoscale confinement inside zinc-air batteries further decreases the freezing point; a 10 nm diameter capillary pore can suppress the local freezing point of the electrolyte by ∼10 °C. Finally, we map out the equilibrium mol% ice as a function of temperature, concentration, and confinement. This study provides insight that can be used to design specialized electrolytes for low temperature applications.