New insights into Li-argyrodite solid-state electrolytes based on doping strategies

Sulfide solid-state electrolytes (SSEs), as the most important component of all-solid-state batteries (ASSBs), have a profound impact on their performance. Among the many sulfide SSEs, Li-argyrodite SSEs have been extensively studied and are considered to be one of the most promising solid sulfide-based Li superionic conductors nowadays. However, the SSEs still have some drawbacks to be addressed, such as limited ionic conductivity at room temperature, incompatible electrode/electrolyte interface, low operating voltage window, and poor air stability. It is found that doping strategies have a non-negligible role in solving the above problems. In this review, we first introduce the crystal structures of Li-argyrodite SSEs and provide a detailed description of Li-ion transport in Li-argyrodite SSEs, followed by a detailed description of structure of the Li-sublattice. Next, the mechanism of doping strategies to enhance the ionic conductivity of Li-argyrodite SSEs is focused. Particular emphasis is provided on the ionic dynamics in doped Li-argyrodite SSEs. In addition, the effects of doping strategies (e.g., soft acid ions and metal oxides) on improving the performance (electrode/electrolyte interface and air stability) of Li-argyrodite SSEs are comprehensively presented. Finally, attractive research directions and perspectives for doped Li-argyrodite SSEs are presented, which are of great significance in guiding the energy conversion and storage of Li-argyrodite-based ASSBs.