The effect of a mixture of an ionic liquid and organic solvent on oxygen reduction reaction kinetics

Li-O₂ batteries attract great attention due to their promising theoretical energy density. One of the main obstacles on the way to achieving high energy density and good cyclability is positive electrode passivation by the Li₂O₂ discharge product as well as the presence of parasitic reactions that degrade electrode and electrolyte materials. To overcome these issues new electrolytes are being extensively searched for to ensure the bulk-mediated mechanism of the oxygen reduction reaction and inhibition of parasitic reactions. Different additives to organic solvents can significantly change the properties of electrolytes. This work is devoted to the effect of ionic liquids (ILs), which are proposed as an additive to the solvent due to their excellent solvation properties, high stability, low volatility and flammability. Using molecular dynamics simulations we investigate mixtures of the Pyr₁₄TFSI ionic liquid and dimethoxyethane (DME) with different volume fractions of the IL. Our calculations show that the presence of the ionic liquid in the electrolyte stabilises solvation shells around the ions, both involved in the oxygen reduction and parasitic reactions, slowing down the kinetics of Li⁺ and O₂^- association. This makes the usage of such mixtures promising for electrolyte design for Li-O₂ batteries.