The effect of competition between solvation and cathode surface adsorption on the kinetics of lithium−oxygen batteries: A model study based on nanoarray electrodes

Abstract

The donor number (DN) of electrolyte solvents was reported to be the key factor determining LiO₂ intermediate solvation and lithium−oxygen battery (LOB) kinetics. In low-DN solvents, LiO₂ tends to adsorb onto cathode surfaces and undergoes surface-mediated reduction to Li₂O₂, while in high-DN solvents, LiO₂ is preferentially solvated and subsequently disproportionates to Li₂O₂. However, prior studies overlooked a critical issue: whether cathode surfaces can provide sufficiently strong adsorption for LiO₂, particularly in low-DN solvents. Herein, this study proposes MnO₂, NiO, and Co₃O₄ nanoarray models alongside carbon nanotubes to simultaneously investigate LiO₂ adsorption on different cathodes and solvent DN effects under consistent cathode architectures. Experimental and theoretical analyses reveal that the discharge of oxygen cathodes involves a competition between the solvation of LiO₂ intermediates and their adsorption on cathodes. When an oxygen cathode has strong adsorption of LiO₂, the adsorption and solvation compete with each other, leading to a solution mechanism in high-DN solvents and a surface mechanism in low-DN solvents. Conversely, if an oxygen cathode shows weak adsorption of LiO₂, a solution mechanism predominately occurs, regardless of whether in high- or low-DN solvents. Thus, when evaluating solvent effects on LOB kinetics, the adsorption capacity of cathode materials must be fully considered.