Effect of postannealing on the properties of a Ta-doped Li₇La₃Zr₂O₁₂ solid electrolyte degraded by Li dendrite penetration

In this study, we investigated the effect of postannealing on the properties of a garnet-type Ta-doped Li6.55La3Zr1.55Ta0.45O12 (Ta-LLZO) ceramic solid electrolyte degraded by lithium (Li) dendrite penetration during electrochemical Li plating and stripping testing in a Li/Ta-LLZO/Li symmetric cell. After the electrochemical testing in the symmetric cell, the Ta-LLZO pellet was taken out of the cell and then annealed at 800 or 900 °C for 4 h in air. It was confirmed that locally discolored spots on the Ta-LLZO surface at which Li dendrite penetrated disappeared after postannealing. The total conductivity of the annealed Ta-LLZO pellet was lower than the initial one but was retained above 10-4 S cm-1 at room temperature. When the soft-shorted or degraded area size by Li dendrite penetration is localized and smaller than the area size for Ta-LLZO, it is expected that the degradation of the conductivity of annealed Ta-LLZO becomes smaller. Obtained electrochemical results indicate the possibility of reusing the degraded garnet-type solid electrolyte by Li dendrite penetration in another all-solid-state Li battery.