Interfacial Modification of Ga-Substituted Li₇La₃Zr₂O₁₂ against Li Metal via a Simple Doping Method

Garnet Li₇La₃Zr₂O₁₂ (LLZO) is considered a promising solid electrolyte for all-solid-state lithium-ion batteries due to its outstanding performance in which Ga-doped LLZO particularly exhibits excellent ionic conductivity. However, the application of Ga-doped LLZO is limited by the interfacial instability between Ga-doped LLZO and Li metal. In this study, Ga³⁺- and Sb⁵⁺-codoped LLZO is prepared using a conventional solid-state reaction method, and the effects of dual-doping on the crystal structure, microstructure, conductivity of LLZO, and battery cycle stability are investigated. The results demonstrate that the introduction of an appropriate amount of Sb⁵⁺ into Ga³⁺-stabilized cubic-phase LLZO promotes grain contact and enhances the total ionic conductivity. The optimized Li_6.3Ga_0.2La₃Zr_1.9Sb_0.1O₁₂ solid electrolyte exhibits the highest total ionic conductivity of 4.65 × 10^-4 S cm^-1 at room temperature. Additionally, the introduction of Sb⁵⁺ suppresses the formation of the LiGaO₂ impurity phase, thereby improving the interface stability between Ga-doped LLZO and the Li metal. The assembled Li||Ga,Sb_0.1-LLZO||Li symmetric cell demonstrates stable cycling for 500 h at room temperature under a current density of 0.13 mA cm^-2. The Li||Ga,Sb_0.1-LLZO||LiFePO₄ full cell delivers a reversible capacity of about 140 mA h g^-1, exhibiting negligible decay after 50 cycles. These findings suggest that the application of Ga-doped LLZO in all-solid-state lithium-ion batteries holds great promise by simply doping Zr sites with high-valence ions.