Understanding the Effect of Doping on the Charging Performance of Li–O2 Batteries: The Role of Hole Polarons and Lithium Vacancies

In this work, we perform density functional theory calculations using the hybrid functional Heyd–Scuseria–Ernzerhof to properly describe the insulating nature of lithium peroxide and study its more energetically favorable surfaces [0001], [11̅00], and [112̅0]. We then analyze how the insulating nature and the correct description of the hole polarons at the Li2O2 surfaces affect the electrochemical steps of Li2O2 decomposition in the charging process of Li–O2 batteries. We then study the effect of doping and propose possible scenarios in which ions such as Na+ or K+ dissolved in the electrolyte can dope and promote the generation of Li vacancies in Li2O2 that, in turn, reduce the energy barrier of the limiting steps of Li2O2 decomposition. The origin of this reduction are the lattice distortions associated with doping that weaken the surface binding.