Single crystal growth and electrochemical studies of garnet-type fast Li-ion conductors

All-solid-state batteries have attracted much attention due to their improved safety and higher energy density as compared to the conventional batteries. Owing to the excellent chemical stability against lithium metal and relatively high ionic conductivity at room-temperature, garnet-type fast lithium ion conductors with three-dimensional lithium ion transport channels are promising solid electrolytes for all-solid-state batteries. In order to better understand the intrinsic lithium-ion transport mechanisms and prevent lithium dendrite formation, it is desired to investigate single-crystal solid electrolytes. In this perspective, we review several methods reported to grow single crystals of garnet-type electrolytes. Pros and cons of different growth methods are discussed. Furthermore, we introduce some case studies on electrochemical properties of garnet-type single crystals. In addition, we provide some perspectives about potential research directions of single-crystal solid electrolytes for all-solid-state batteries.