Structure and Ion Conductivity Study of Argyrodite (Li5.5PS4.5Cl1.5) according to Cooling Method

Abstract

All solid-state batteries (ASSBs) are now anticipated to be an ultimate solution to the persistent safety issues of conventional lithium-ion batteries (LIBs). Contemporary society’s expanding power demands and growing energy consumption require energy storage with greater reliability, safety and capacity, which cannot be easily achieved with current state-of-the-art liquid-electrolyte-based LIBs. In contrast, these conditions are expected to be met by implementing ASSBs with high-performance solid-state electrolytes (SSEs). In this work, we altered the microscopic structure and Li diffusional behaviors of argyrodites (Li6-xPS5-xCl1+x), which were precisely monitored with cooling protocols. It was shown that, at the cooling speed of -3 ^oC·h^-1, as the cooling rate decreased, impurities in Li5.5PS4.5Cl1.5 such as LiCl and Li3PO4 gradually diminished and eventually disappeared. At the same time, differences in the lattice sizes of Li5.5PS4.5Cl1.5 crystallites gradually decreased, resulting in a single phase Li5.5PS4.5Cl1.5. It was also found that the Cl content of the 4d crystallographic sites increased, eventually contributing to the improvement in ionic conductivity. This work also revealed the effect of cooling rates on the crystallographic atomic arrangements, which became weaker as a decrease in x. The correlations between ionic conductivities and structural features were experimentally verified via XRD and solid-state NMR studies.