Superionic conduction and interfacial properties of the low temperature phase Li7P2S8Br0.5I0.5

Sulfide-based solid electrolytes have attracted much attention for their potential application in high energy and power bulk-type all-solid-state lithium batteries, due to their excellent transport properties and favorable mechanical properties. The Li10GeP2S12-type materials with extremely high ionic conductivity have been demonstrated in all-solid-state cathodes, however they cannot be deployed directly in common anodes due to the interfacial instability. An electrolyte stable with anodes is urgently needed for construction of all-solid-state batteries. In this work, we explore the phase and transport properties of mechanically-milled Li7P2S8Br0.5I0.5, with emphasis on the favorable kinetics at Li metal anode. The low temperature crystalline phase Li7P2S8Br0.5I0.5 (LT-LPSBI) has exceptionally high ionic conductivity of 4.7 mS/cm at room temperature. Moreover, the LT-LPSBI supports long-term Li cycling at 0.5 mA cm−2 with low and stable interfacial resistance (5 Ω cm2). Transport phenomenon of Li/LT-LPSBI interface and cycling behavior of Li symmetric cells are studied and discussed in detail.