(Invited) Complex Ion Migration Mechanisms in Glassy Lithium Solid Electrolytes

Abstract

Sulfur-based glasses have reemerged as promising candidates for use as solid electrolytes in Li-based batteries. Nevertheless, due to their amorphous structure, the ion migration mechanisms that underlie the high Li-ion conductivity observed in these glasses remain poorly understood. The present study employs ab initio molecular dynamics to characterize the local structure and migration mechanisms in the prototype Li-ion conducting glass, 75Li2S–25P2S5. A computational model of the amorphous structure was generated and is shown to closely match the measured neutron pair distribution function. This structure data indicates that Li-ions experience varying coordination environments, with typical Li-S coordination numbers ranging from 3 to 5. Lithium migration is observed to occur via a complex mechanism involving the concerted motion of multiple neighboring lithium ions. Additionally, the PS4 anion sublattice plays an active role in these migration events via the ‘paddle-wheel’ mechanism: Li motion is dynamically coupled to the rotational properties of the PS4 tetrahedra. The behavior of the amorphous phase contrasts with that of the crystalline analogue, where contributions from anion dynamics are limited. These atomic-scale observations suggest that Li-ion transport in S-based glasses results from the combined effects of cooperative cation motion and dynamic anion coupling.