Li and Na Diffusion in TiO2 from Quantum Chemical Theory versus Electrochemical Experiment

Diffusion of Li and Na ions in TiO2, anatase, has been studied using theor. (quantum chem. ab initio periodic Hartree-Fock and a modified semiempirical INDO) as well as electrochem. (chronocoulometry) methods. On the basis of the theor. calcns., the geometry of equil. and transition states for the impurities as well as the cryst. framework are analyzed and discussed. The calcd. activation energies for Li+ and Na+ diffusion were found to be only slightly higher than 0.5 eV by both theor. methods. The agreement of either theor. method with the electrochem. expts., 0.60 and 0.52 eV for Li+ and Na+, resp., is also remarkably good.