Defect chemistry engineering of Ga-doped garnet electrolyte with high stability for solid-state lithium metal batteries

Ga-doped Li₇La₃Zr₂O₁₂ (Ga-LLZO) has long been considered as a promising garnet-type electrolyte candidate for all-solid-state lithium metal batteries (ASSLBs) due to its high room temperature ionic conductivity. However, the typical synthesis of Ga-LLZO is usually accompanied by the formation of undesired LiGaO₂ impurity phase that causes severe instability of the electrolyte in contact with molten Li metal during half/full cell assembly. In this study, we show that by simply engineering the defect chemistry of Ga-LLZO, namely, the lithium deficiency level, LiGaO₂ impurity phase is effectively inhibited in the final synthetic product. Consequently, defect chemistry engineered Ga-LLZO exhibits excellent electrochemical stability against lithium metal, while its high room temperature ionic conductivity (∼ 1.9 × 10⁻³ S⋅cm⁻¹) is well reserved. The assembled Li/Ga-LLZO/Li symmetric cell has a superior critical current density of 0.9 mA⋅cm⁻², and cycles stably for 500 hours at a current density of 0.3 mA⋅cm⁻². This research facilitates the potential commercial applications of high performance Ga-LLZO solid electrolytes in ASSLBs.