Elucidating the Solubility and Diffusivity of Atmospheric Gases in a Wide Variation of Liquid Electrolytes for Lithium-Air Batteries

Abstract

Due to their high theoretical energy density, Li–O2 and Li–air batteries are considered as a promising alternative to Li-ion batteries, especially for mobile applications. However, dissolved gases in the liquid electrolyte, in particular O2, can be involved in detrimental side reactions at the lithium anode. Moreover, CO2 that can form from side reactions with the electrolyte or the cathode material, and N2 from the ambient air might be dissolved in the electrolyte.In order to evaluate the impact of these dissolved gases on the stability of the anode and to know their concentrations in possible side reactions, the solubility and the diffusion coefficient for each gas in the electrolyte are crucial parameters to know.In this work, we utilize gas uptake measurements to systematically determine the diffusion coefficients and Henry’s law solubility constants of O2, N2 and CO2 in different ether- and DMSO-based electrolytes and pure solvents. Additionally, we calculate the diffusion coefficient with molecular dynamics simulations and show good qualitative agreement between simulations and experimental results. We discuss the influence of solvent parameters, such as surface tension and viscosity, on the solubility and the diffusivity as well as the impact of different conducting salts. All investigated conducting salts reduce the diffusivity of the gases; however, we observe the solubility can both decrease or increase, depending on the solvent, the gas and the molecular structure of the salt. Therefore, we emphasize that both components, solvent and conducting salt, have to be considered for optimizing the gas transport properties of the electrolyte for Li–O2 and Li–air batteries.