Enhancing the ionic conductivity and stabilizing cubic structure of garnet-type Li6.25-xAl0.25La3Zr2-xTaxO12 by Al/Ta co-doping

The inorganic solid electrolytes Li6.25-xAl0.25La3Zr2-xTaxO12 (LALZT) with various Ta contents (x) are synthesized using conventional solid-state reaction method at 1200 ​°C for different holding times. The effect of holding time and Al/Ta co-doping on the crystal structure, microstructure and ionic conductivity of the LALZT solid electrolytes is discussed. The LALZT powder with a fine particle size and narrow particle distribution is prepared by the high-energy ball milling. Suitable Al/Ta doping stabilizes the cubic phase and enhances the ionic conductivity of the LALZT. The short holding time is 6 ​h due to the equal ionic conductivity for the LALZT samples sintered for 6 ​h or 10 ​h by the solid-state reaction method. The highest ionic conductivity can be obtained for the optimized composition of Li5.85Al0.25La3Zr1.6Ta0.4O12. The excellent ionic conductivity indicates that Al/Ta co-doped LALZT could be a promising electrolyte candidate for all-solid-state Li-ion batteries in practical application.