Review on Impurity and Conductivity Issues of Garnet Type Li7La3Zr2O12: Mechanisms, Solutions, and Perspectives

Garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO) is the most suitable choice for an all-solid-state battery (ASSB) electrolyte. However, upon air/moisture exposure LLZO sufferers problems like surface contamination and poor ionic conductivity. This eventually leads to issues like (a) sample degradation, (b) high interfacial resistance, (c) low voltage window, (d) reduced capacity and energy density, (e) poor power density and rate performance, and limited cycle life. In the present work, we have critically reviewed recent research progress on (i) the surface contamination removal process and (ii) the doping effect in pristine garnet ceramics. This review mainly focuses on the changes in electrical properties of surface-treated and untreated LLZO. Finally, a comparative study describes the best practices to avoid surface contamination and improve conductivity.