A bird's-eye view of Li-stuffed garnet-type Li7La3Zr2O12 ceramic electrolytes for advanced all-solid-state Li batteries

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.