Formation Mechanism of β-Li₃PS₄ through Decomposition of Complexes

β-Li₃PS₄ is a solid electrolyte with high Li⁺ conductivity, applicable to sulfide-based all-solid-state batteries. While a β-Li₃PS₄-synthesized by solid-state reaction forms only in a narrow 300-450 °C temperature range upon heating, β-Li₃PS₄ is readily available by liquid-phase synthesis through low-temperature thermal decomposition of complexes composed of PS₄^3- and various organic solvents. However, the conversion mechanism of β-Li₃PS₄ from these complexes is not yet understood. Herein, we proposed the synthesis mechanism of β-Li₃PS₄ from Li₃PS₄·acetonitrile (Li₃PS₄·ACN) and Li₃PS₄·1,2-dimethoxyethane (Li₃PS₄·DME), whose structural similarity with β-Li₃PS₄ would reduce the nucleation barrier for the formation of β-Li₃PS₄. Synchrotron X-ray diffraction clarified that both complexes possess similar layered structures consisting of alternating Li₂PS₄^- and Li⁺-ACN/DME layers. ACN/DME was removed from these complexes upon heating, and rotation of the PS₄ tetrahedra induced a uniaxial compression to form the β-Li₃PS₄ framework.