Origin of Fast Ion Conduction in Li10GeP2S12, a Superionic Conductor

Abstract

The discovery of additional sites in Li10GeP2S12 (LGPS) has suggested the possibility of cross channel diffusion pathways. Here we present a first principles density functional theory based study of ion migration in LGPS. We find that energy barrier for ion migration depends significantly on the c channel population, local Li environment and the hopping mechanism. A novel mechanism of correlated diffusion between the c channel and ab plane is found with a significantly lower energy barrier. The novel mechanism of Li diffusion can work even if some channels gets blocked after repeated cycling, thereby, providing alternate pathways for Li diffusion. We calculate the overall energy barrier by taking a grand canonical ensemble average of the energy barriers. The computed energy barrier of 239 meV is in remarkable agreement with the experimentally observed energy barrier of 240 meV. The study explains the overall diffusion mechanism in LGPS and is relevant for other solid electrolytes as well. Figure 1