The electronic structure was converged to 1 × 10 -5 eV, applying a plane-wave cutoff energy of 550 eV. The migration barriers for intercalation and bulk diffusion were obtained by applying the climbing image Nudged Elastic Band (NEB) method. Most NEB calculations were performed using three distinct images along the pathway. The ones which required more detailed calculations, were found in preliminary setups, to be symmetrical with a meta stable state in the middle and were thus calculated in a symmetrical fashion, form the start point to the meta stable intermediate state. All forces on the atoms were converged within 0.05 eV Å-1 .