Simulated electrolyte-metal interfaces -- Li$_3$PO$_4$ and Li

There has recently been a lot of interest in solid electrolyte materials such as LiPON developed at Oak Ridge National Laboratory\footnote{J. B. Bates, N. J. Dudney, and co-workers, {\em{Solid State Ionics}}, {\bf{53-56}}, 647-654 (1992).} for use in Li-ion batteries and other technologies. We report on the results of our model calculations on idealized interfaces between Li$_3$PO$_4$ and Li metal, studying the structural stability and the ion mobility, using first-principles density functional techniques with the {\em{PWscf}} and {\em{pwpaw}} codes.\footnote{http://www.pwscf.org and http://pwpaw.wfu.edu.} Starting with a supercell constructed from Li$_3$PO$_4$ in its crystalline $\gamma$-phase structure and several layers of Li metal, we used optimization and molecular dynamics techniques to find several meta-stable configurations. The qualitative features of the results are consistent with experimental evidence that the electrolyte is quite stable with respect to Li metal.\footnote{N. J. Dudney in Gholam-Abbas Nazri and Gianfranco Pistoia, Eds., {\em{ Lithium Batteries: Science and Technology}}, Chapt. 20, pp. 623$-$642, Kluwer Academic Publishers, 2004. ISBN 1-4020-7628-2.} In addition to stability analyses, we plan to study Li-ion diffusion across the interface.