Computational Study of the O₂/Li⁺-O₂^- Redox Couple in Li-Air Batteries

Lithium-air batteries are an active area of research because of their potential to have a much higher energy density (per unit mass) than traditional lithium-ion batteries but are not yet commercially viable due to poor efficiency, high charging voltages, and low cycle lifetimes. It has been found experimentally that in Li-air batteries with aprotic solvents the O₂ reduction starts when superoxide (O₂^-) forms in solvent and reacts with Li⁺ to form lithium superoxide (Li⁺-O₂^-) [1]. Solid Li₂O₂ is then formed as the final discharge product on the cathode. Recent experimental work has suggested that a better understanding of the factors governing the behavior of the lithium superoxide in solvent could help control the discharge at the cathode [1]. We have used a combination of density functional theory calculations and ab-initio molecular dynamics simulations to model the interactions of the Li⁺ and O₂^- ions in solvent and study properties such as the clustering behavior of Li⁺-O₂^-. [1] D. G. Kwabi, V. S. Bryantsev, T. P. Batcho, D. M. Itkis, C. V. Thompson, Y. Shao-Horn, Angew. Chem. Int. Ed. 2016, 55, 3129.