The potential of hydrophobic membranes in enabling the operation of lithium-air batteries with ambient air

Lithium-air batteries are presented in the literature as a candidate for electrochemical energy storage because of their potentially high energy density. Part of this high energy density comes from the fact that one of its components – oxygen – can be sourced from the air. However, when operating with ambient air, these batteries are exposed to contamination with water, a component that may damage the Li electrode. Bearing this in mind, this work analyzes the potential of hydrophobic membranes in allowing lithium-air batteries to work with ambient air containing moisture. For this investigation, a model that includes the influence of water concentration in the electrolyte (LiClO4 in dimethyl sulfoxide) on the morphology of the discharge product was developed based on experimental data. Results demonstrate that membrane permeability should be lower than currently available technologies to satisfactorily reduce the increase in water concentration over time. According to simulation results, membrane permeability for water should be below 0.2 mg m−2 d−1 for a current density of 0.25 A m−2 or 1.6 mg m−2 d−1 for a current density of 0.75 A m−2 to allow a water concentration increase of only 1 ppm after each discharge. This severe limitation in membrane permeability requirement indicates that a moisture-controlled O2 source for Li-air or Li-O2 batteries in a closed system might be preferred to preserve electrolyte properties.