PNNL

Abstract

We report the findings of a computational investigation of defect migration in two lithium aluminate ceramics using Coulombic and Buckingham potential parameters from the literature. We first established the validity of the potential for both LiAlO2 to LiAl5O8 through good agreement between the calculated physical quantities (density, crystallinity, bond lengths and melting point) and their experimental values. Subsequently we examined the Li+ diffusion properties in the two systems and found that Li ion diffusion is 2 orders of magnitude slower in LiAl5O8 (D0 = 5.34 e-12 m2/s) as compared to that in LiAlO2 (D0 = 4.02 e-10 m2/s) at 600 K. The lithium (vacancy) migration barrier in LiAl5O8 (4.15 eV) is 3 times that in LiAlO2 (1.31 eV). Pair correlation functions indicate that Li-O interactions could be stronger in the Li-O6 octahedra of LiAl5O8 than those in Li-O4 tetrahedra of LiAlO2. The stronger Li-O bond may retard the Li migration in LiAl5O8 thereby making it a more resistant to atomic displacement than LiAlO2. However, the Li+ interstitial migration barriers in both ceramics show that the migration along quadrangular channels in LiAlO2 is energetically more expensive (1.41 eV) than the tetrahedral-octahedral migration pathway in LiAl5O8 (0.42 eV), thereby providing first evidence of better dynamic annealing in LiAl5O8.