Understanding the effect of doping on the charging performance of the Li-O2 battery: the role of hole polarons and lithium vacancies

In this work, we perform DFT calculations using the hybrid functional HSE to properly describe the insulating nature of lithium peroxide and study its more energetically favourable surfaces [0001], [1-100] and [11-20]. We then analyse how the insulating character and the correct description of the hole polarons at the Li2O2 surfaces affect the electrochemical steps of Li2O2 decomposition in the charging process of the Li-O2 battery. We then study the effect of doping and propose possible scenarios in which the ions as Na+ or K+ dissolved in the electrolyte can dope and promote Li vacancies generation in the Li2O2 that, in turn, reduce the energy barrier of the limiting steps of the Li2O2 decomposition. The origin of this reduction are the lattice distortions associated with doping that weaken the surface binding.