Batteries with a solid-state electrolyte and a Li anode (solid-state Li batteries, SSLBs) are being considered to replace conventional organic liquid-based Li-ion batteries due to SSLBs’ promise of higher energy density and improved safety. The crucial component in SSLBs is the solid-state electrolyte which must fulfill requirements in Li-ion conductivity, electrochemical stability, and chemical stability towards the cathode and Li anode. Recently, much attention has been given to a class of ceramics with a garnet-type structure, specifically on compositions based on Li-stuffed Li7La3Zr2O12 (LLZO) because they fulfill all the enumerated requirements for a solid-state electrolyte. In this review, we update the progress and analyze the trends in the three main approaches to realize the technological application of LLZO as an electrolyte in SSLBs: (i) crystal structure and lithium content control by doping to enhance Li-ion conductivity of LLZO, (ii) microstructure and dimension control by material processing and thin-film fabrication to reduce electrolyte resistance, and (iii) LLZO–electrode interface tuning to reduce interfacial resistance and improve battery performance. Finally, we offer our perspectives on research paths toward the realization of practical batteries with LLZO solid electrolytes.
