Electrode/Electrolyte Interface in the Li–O2 Battery: Insight from Molecular Dynamics Study

Abstract

In this paper, for the first time, we report the results of molecular dynamics simulation of the electrode/electrolyte interface of a Li–O2 cathode under potentials close to experimental values in 1 M dimethyl sulfoxide (DMSO) solution of LiPF6 salt. Electric potential profiles, solvent structuring near the electrode surface, and salt ion distributions are presented and discussed here as well as potentials of mean force (PMFs) of oxygen and its reduction products. The latter would be of a great use for future theoretical studies of reaction kinetics as PMF is essentially the work term required for reaction rate constant estimations. At the electrode/electrolyte interface under realistic potentials, oxygen anions are effectively pushed out of the reaction layer, making the second reduction of superoxide anion hardly probable. This indicates that the main cause of the electrode surface passivation should be lithium superoxide presence near the electrode surface. The way to suppress the passivation is to shift the equilibrium Ȯ2– + Li+ ⇌ LiO2 to the side of separately solvated ions, for example, by using solvents resulting in lower free energy of the ions. This conclusion is in agreement with the hypothesis stating that high donor number solvents lead to dominant solution Li2O2 growth and significantly higher cell discharge capacities.