Computational studies of solubilities of LiO₂ and Li₂O₂ in aprotic solvents

Knowledge of the solubilities of Li₂O₂ and LiO₂ in aprotic solvents is important for insight into the discharge and charge processes of Li-O₂ batteries, but these quantities are not well known. In this contribution, the solvation free energies of molecular LiO₂ and Li₂O₂ in various organic solvents were calculated using various explicit and implicit solvent models, as well as ab initio molecular dynamics (AIMD) methods. The solvation energies from these calculations along with calculated lattice energies of Li₂O₂ and LiO₂ were used to determine the solubility of bulk LiO₂ and Li₂O₂. The computed solubility of LiO₂ (1.8 × 10^-2 M) is about 15 orders higher than that of Li₂O₂ (2.0 × 10^-17 M) due to a much less negative lattice energy of bulk LiO₂ compared to that of Li₂O₂. The difference in solubilities between LiO₂ and Li₂O₂ likely will affect the nucleation and growth mechanisms and resulting morphologies of the products formed during battery discharge, influencing the performance of the battery cell. The calculated LiO₂ and Li₂O₂ solubilities provide important information for fundamental studies of discharge and charge chemistries in Li-O₂ batteries.