Electrolytes for Li-ion all-solid-state batteries: a first-principles comparative study of Li10GeP2O12 and Li10GeP2S12 in the LISICON and LGPS phases

TL;DR

This study uses first-principles molecular dynamics to compare lithium-ion diffusion in oxide and sulfide phases of Li10GeP2O12 and Li10GeP2S12, revealing potential new solid electrolytes with high conductivity.

Contribution

It provides a comparative analysis of Li-ion diffusion in different phases of LGPO and LGPS using advanced simulations, including the first report of tetragonal LGPO's properties.

Findings

Orthorhombic LGPO is much less conductive than LGPS.

Tetragonal LGPO shows high conductivity comparable to LGPS.

Tetragonal LGPO could be a promising new Li-ion conductor if synthesized.

Abstract

In this work we address Li-ion diffusion in thio-LISICON materials and in their oxide counterparts, exploring both the orthorhombic and tetragonal phases of Li10GeP2S12(LGPS) and Li10GeP2O12(LGPO) through extended Car-Parrinello molecular dynamics in the canonical and isobaric-isothermal ensemble. The (quasi-)orthorhombic and tetragonal phases are studied both for the oxide and for the sulfide, with the aim of comparing their conductivity with the same approach; out of these four case studies, tetragonal LGPO has not been reported and, while dynamically stable, it sits (0.04 Ha/formula unit) above orthorhombic LGPO. We calculate activation energies for diffusion of 0.18 eV and 0.23 eV for tetragonal and orthorhombic LGPS, and of 0.22 eV and 0.34eV for tetragonal and orthorhombic LGPO. In line with experiments, we find orthorhombic LGPO orders of magnitude less conductive, at room temperature, than the two sulfide systems. However, this is not the case for tetragonal LGPO, which, although less stable than its orthorhombic allotrope, shows at room temperature a conductivity comparable to orthorhombic and tetragonal LGPS, and, if synthesized, could make a very attractive Li-ion conductor.