Li6PS5I

Li6PS5I is a lithium argyrodite solid electrolyte with the formula Li6PS5I. It is part of the Li6PS5X family of materials (X = Cl, Br, I), which share a cubic, sulfur-rich framework built from PS4^3- tetrahedra and mobile Li+ ions. In the crystal, the PS4 tetrahedra form a three-dimensional anionic network, while Li+ occupies multiple interstitial sites that create diffusion pathways. The iodide anions sit in specific lattice positions and influence Li+ mobility and the overall conductivity.

Room-temperature ionic conductivity for Li6PS5I is typically on the order of 10^-3 S/cm, with activation energies commonly reported in the range of around 0.25–0.4 eV. These materials are among the higher-conductivity sulfide-based solid electrolytes at ambient conditions, and the halide composition can tune the diffusion landscape.

Synthesis is usually performed by solid-state reaction of Li2S, P2S5, and LiI under inert atmosphere at elevated temperatures, followed by annealing. Mechanochemical methods such as high-energy ball milling can also be used to prepare precursor mixtures before heat treatment.

Applications center on all-solid-state lithium batteries. Li6PS5I serves as a solid electrolyte enabling Li+ transport between anodes and cathodes, including configurations with lithium metal anodes. Interface compatibility, grain boundary resistance, and chemical stability with electrodes and moisture are important considerations, and surface modification or composite approaches are often pursued to improve performance.

Handling of Li6PS5I requires care: sulfide-based electrolytes are generally moisture- and air-sensitive and can release toxic gases such as H2S on hydrolysis, so synthesis and storage are typically conducted in controlled, inert environments.