Dual Substitution and Spark Plasma Sintering to Improve Ionic Conductivity of Garnet Li7La3Zr2O12

Garnet Li7La3Zr2O12is one of the most promising solid electrolytes used for solid-state lithium batteries. However, low ionic conductivity impedes its application. Herein, we report Ta-doping garnets with compositions of Li7-xLa3Zr2-xTaxO12(0.1 ≤ x ≤ 0.75) obtained by solid-state reaction and free sintering, which was facilitated by graphene oxide (GO). Furthermore, to optimize Li6.6La3Zr1.6Ta0.4O12, Mg2+was select as a second dopant. The dual substitution of Ta5+for Zr4+and Mg2+for Li+with a composition of Li6.5Mg0.05La3Zr1.6Ta0.4O12showed an enhanced total ionic conductivity of 6.1 × 10−4S cm−1at room temperature. Additionally, spark plasma sintering (SPS) was applied to further densify the garnets and enhance their ionic conductivities. Both SPS specimens present higher conductivities than those produced by the conventional free sintering. At room temperature, the highest ionic conductivity of Li6.5Mg0.05La3Zr1.6Ta0.4O12sintered at 1000 °C is 8.8 × 10−4S cm−1, and that of Li6.6La3Zr1.6Ta0.4O12sintered at 1050 °C is 1.18 × 10−3S cm−1.Keywords:garnet;dual substitution;spark plasma sintering;conductivity