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.