Li₁₅P₄S₁₆Cl₃, a Lithium Chlorothiophosphate as a Solid-State Ionic Conductor

Tremendous efforts have been devoted to the design of solid Li⁺ electrolytes and the development of all-solid-state batteries. Compared with conventional Li-ion batteries, which use flammable liquid organic electrolytes, all-solid-state batteries show significant advantages in safety. In this work, a novel lithium chlorothiophosphate compound, Li₁₅P₄S₁₆Cl₃, is discovered. The crystal structure and electrochemical properties are investigated. Li₁₅P₄S₁₆Cl₃ can be synthesized as a pure phase via a facile solid-state reaction by heating a ball-milled mixture of Li₂S, P₂S₅, and LiCl at 360 °C. The crystal structure of Li₁₅P₄S₁₆Cl₃ was refined against neutron and synchrotron powder X-ray diffraction data, revealing that it crystallizes in the space group I4̅3d. The Li⁺ transport in Li₁₅P₄S₁₆Cl₃ was also investigated by multiple solid-state NMR methods, including variable-temperature NMR line-shape analysis, NMR relaxometry, and pulsed-field-gradient NMR. Li₁₅P₄S₁₆Cl₃ shows good thermodynamic stability and can be synthesized at relatively low temperature. Although it exhibits a low ionic conductivity at room temperature, it can serve as a new motif crystal structure for the design and development of new solid-state electrolytes.