Anisotropic Li diffusion in pristine and defective ZnO bulk and (10[formula omitted]0) surface

Abstract

We study the Li interstitial diffusion in pristine and defective ZnO bulk and (101¯0) surface by means of first-principles density functional theory (DFT) coupled with the Nudged Elastic Band (NEB) calculations. We consider three types of point defects, i.e., oxygen vacancy (Ovac), Zn vacancy (Znvac) and ZnO vacancy pair (ZnOvac-pair) and investigate their individual effect on the energy barrier of Li interstitial diffusion. Our results predict that Ovac and Znvac lower the Li diffusion energy barrier as compared to the pristine ZnO case. However, we further find that Li interstitial, on the other hand, may possibly be trapped inside the Znvac subsequently forming the LiZn substitutional type of defect. The similar behavior also observed for Li interstitial in the vicinity of Zn-Ovac_pair though with less change of Li diffusion barriers as compared to the other two cases. For Li diffusion on the ZnO surface, our results indicate that Ovac imposes similar effect as in the bulk case; it lowers the energy barriers for Li to diffuse outward (inward) from (to) ZnO sub-surface lattice. Our results indicate that among the three considered defects only Ovac shows possible enhancement of the kinetics of Li diffusion inside the bulk and on the surface of ZnO.