Elucidating the role of multi-scale microstructures in Li7La3Zr2O12 based all-solid-state lithium batteries

Utilizing lithium metal anodes with solid-state electrolytes (SSEs) to construct all-solid-state lithium batteries (ASSLBs) is a promising approach, which offers high energy density and safety. The SSEs play an integral role in ASSLBs, and the oxide garnet-type Li7La3Zr2O12 (LLZO) is widely used as electrolyte material due to its high Li+ conductivity and wide electrochemical window. However, many issues in LLZO still need to be addressed, like the formation of Li2CO3 in air, interface contact with electrodes, and the growth of Li dendrites. We approach this review from the perspective that "structure determines performance", elucidating the relationship between multi-scale microstructures (doping defects, grain boundary, surface and interface) and four key performances in batteries (Li+ conductivity, air stability, Li dendrites and cathode compatibility), analyzing the mechanisms of performances degradation induced by microstructures and summarizing various microstructures modification strategies that enhance performances, with the aim of constructing high-performance LLZO-based ASSLBs. Finally, we outline future research directions for LLZO, including the development of high-entropy LLZO SSEs, in-depth studies of grain boundary, advanced characterization and extra performance testing for LLZO evaluation, and feasible strategies in applications of LLZO-based ASSLBs.