Figure shows the results obtained for a potential U=0V, using the GGA (black line) and HSE (red line) functionals. First of all, at U=0V, as expected, the whole reaction is endothermic. In both methods, the initial step in the reaction path is the formation of a lithium vacancy (V Li ). Within GGA the extra charge left behind by V Li is wide spread along the surface, the surface turns metallic in this step. See the corresponding DOS in Figure in the SI file. On the contrary, a hole gets trapped at a surface O 2 dimer within HSE, forming a polaron. This step has a higher energy barrier within HSE than within GGA, since the former functional leads to an extra elastic cost. The polarons are again schematized as purple bonded O 2 dimers in the insets of Figure . The second step is the formation of a second V Li that gives rise to another polaron within HSE whereas within GGA more metallic states are generated (see Figure in the in SI file). In general, the second V Li has a lower formation energy than the first one because the surface structure was already distorted by the first vacancy; the system is less bound. The subsequent two reaction steps are the liberation of two LiO 2 . It is important to remark that these steps present a higher energy barrier for the functional GGA. The reason for this is that the energy cost is comparatively larger within GGA due to the overbinding energy of the delocalized charge. On the other hand, within HSE the system gets rid of the elastic cost of one polaron in each of the last two steps so that the final reaction free energy turns out to be smaller than within GGA. In particular, the last step is the limiting one and will determine the value of the overpotential. In the present work, we do not aim to obtain an absolute value of the overpotential because we are not considering other complex details such as the role of the solvent, the Li and O 2 diffusion and charge transport through the Li 2 O 2 , among others. The main message of this section is that some care should be taken when describing the recharge process within GGA because the energy cost of the limiting step is overestimated.