Experimental and Computational Study of Mg and Ta‐Doped Li₇La₃Zr₂O₁₂ Garnet‐Type Solid Electrolytes for All‐Solid‐State Lithium Batteries

Abstract Garnet‐type Li₇La₃Zr₂O₁₂ electrolytes have garnered significant attention as promising solid‐state electrolyte candidates in all‐solid‐state lithium batteries (ASSLBs). However, its susceptibility to forming Li₂CO₃ upon atmospheric exposure leads to performance degradation, limiting its application. This study introduces a co‐doping strategy of Mg and Ta to enhance the properties of garnet electrolytes. Pure cubic Mg and Ta‐doped LLZO electrolytes are successfully synthesized using the solid‐state reaction method. Experimental results, coupled with density functional theory (DFT) calculation, reveal that Mg²⁺ doping occurs primarily at the La site (24c). This substitution, given the substantial disparity in ionic radii between Mg²⁺ and La³⁺, effectively narrows the transport bottleneck for Li‐ions, resulting in a decreased ionic conductivity and an increased activation energy. Li₆.₆La₂.₈Mg₀.₂Zr₁.₄Ta₀.₆O₁₂ exhibits a relative density of ≈92.6%, demonstrating outstanding performance with a room temperature ionic conductivity of 4.31 × 10⁻⁴ S cm⁻¹ and low electronic conductivity of 2.48 × 10⁻⁸ S cm⁻¹. Notably, after 4 months of atmospheric exposure, its ionic conductivity decreased to ≈78% of the initial value, attributable to Li₂CO₃ formation. Furthermore, the material demonstrated exceptional long‐term cycle stability over 1000 h at a current density of 0.1 mA cm⁻² at 25 °C, indicating effective suppression of Li dendrite formation.