Ab initio molecular dynamics study of 1-D superionic conduction and phase transition in β-eucryptite

Abstract

β-Eucryptite (LiAlSiO₄) is a potential electrolyte for Li-ion batteries due to its high Li-ion conductivity and very small volume thermal expansion coefficient. We have performed ab initio molecular dynamics simulations of β-eucryptite to study the origin of high temperature superionic phase transition in this material. The simulations are able to provide microscopic understanding of the one-dimensional superionicity that occurs along the hexagonal c-axis and is associated with the order–disorder nature of the phase transition. The Li ionic conductivity is found to increase due to the anisotropic negative thermal expansion along the hexagonal c-axis. The introduction of defects in the crystal, such as excess Li in interstitial sites, Li vacancy and O vacancy, is found to significantly increase the ionic conductivity and hence might reduce the temperature of the superionic phase transition in this material.