The synergetic modification on ionic conductivity and air stability of Ga³⁺ and Ta⁵⁺ co‐doped Li₇La₃Zr₂O₁₂ (LLZO).

The garnet‐type oxide Li7La3Zr2O12 solid‐state electrolytes (SSEs) are considered as a reliable option in all‐solid‐state lithium batteries (ASSLBs) due to its excellent properties. However, it still faces challenges such as limited ionic conductivity and low air stability. In this work, Ga3+ and Ta5+ co‐doped samples Li7−3x−yGaxLa3Zr2−yTayO12 (GaxTay‐LLZO) synthesized via the solid‐state method are demonstrated to stabilize the cubic phase, regulate the concentration of Li vacancies in LLZO, and improving the Li+ transport channels. As a result, the Ga0.1Ta0.3‐LLZO sample achieves a high conductivity of ∼1 mS cm−1. Furthermore, we discovered that in addition to the previously reported effects of decreasing grain boundary density and the inert LiGaO2 secondary phase at grain boundaries, the synergistic effect of introducing multiple dopant ions, which enhances lattice stability, is also a key factor contributing to improved air stability. Our findings demonstrate that co‐doping strategy with Ga3+/Ta5+ is an effective method for simultaneously enhancing conductivity and air stability of LLZO, laying solid foundation for the application of SSEs in ASSLBs. [ABSTRACT FROM AUTHOR]