Formation Mechanism of β-LiPS through Decomposition of Complexes.

β-LiPS is a solid electrolyte with high Li conductivity, applicable to sulfide-based all-solid-state batteries. While a β-LiPS-synthesized by solid-state reaction forms only in a narrow 300-450 °C temperature range upon heating, β-LiPS is readily available by liquid-phase synthesis through low-temperature thermal decomposition of complexes composed of PS and various organic solvents. However, the conversion mechanism of β-LiPS from these complexes is not yet understood. Herein, we proposed the synthesis mechanism of β-LiPS from LiPS·acetonitrile (LiPS·ACN) and LiPS·1,2-dimethoxyethane (LiPS·DME), whose structural similarity with β-LiPS would reduce the nucleation barrier for the formation of β-LiPS. Synchrotron X-ray diffraction clarified that both complexes possess similar layered structures consisting of alternating LiPS and Li-ACN/DME layers. ACN/DME was removed from these complexes upon heating, and rotation of the PS tetrahedra induced a uniaxial compression to form the β-LiPS framework.