Quantitative elucidation of cathode reaction mechanisms in Li-O₂ batteries within high donor number solvents

Abstract

Lithium-oxygen cells, known for their exceptional energy density, have complex reaction processes making a quantitative elucidation of the reaction mechanism, especially at the cathode quite difficult. Using density functional theory (DFT) combined with nudged elastic band (NEB) calculations, and cyclic voltammetry (CV) experiments in high donor number solvents, we developed a numerical computational model that elucidates the primary reaction pathway at the cathode. This study highlights two key reasons for the voltage gap between the charging and discharging phases: the shift in lithium superoxide's reaction voltage from lithium peroxide's thermodynamic equilibrium voltage, and the extra energy needed to electrolyze nucleated lithium peroxide. This study shows that by optimizing the high donor number solvent system and optimum battery design, up to 78.9 % of theoretical specific energy can be achievable, signaling significant prospects for advancing Li-O₂ battery technology.