Super-Ionic Conduction in Solid-State Li₇P₃S₁₁-Type Sulfide Electrolytes

Here, we examine the intrinsic ion conduction properties of Li7P3S11-type materials, one of the important solid electrolytes for lithium batteries, through a comprehensive computational investigation on the interplay among the crystal structure, defects, and diffusion mechanism. Our extensive ab initio molecular dynamics calculations suggest that the Li7P3S11 crystal frame is inherently flexible with readily-fluctuating P2S7 polyhedra and possesses high density of interstitial sites, which flatten the overall energy landscape for ion migration and provide higher degrees of freedom for ion movement. Statistical analysis also presents that ionic conduction in Li7P3S11 is negligibly influenced by the presence of defects and the change of charge carrier concentrations. It implies that the intrinsic high ionic conductivity of Li7P3S11 can be easily preserved in various chemical conditions during the synthesis or electrochemical operations under Li-rich or vacancy-rich conditions. This study broadens our understanding on the Li7P3S11-type materials with respect to the crystal structure, defects, and superionic conductions, which would aid in the further development of this class of materials