Sol-gel synthesis of a Fe-doped cubic phase Li₇La₃Zr₂O₁₂ Solid State Electrolyte

Cubic Li₇La₃Zr₂O₁₂ (LLZO) exhibits high ionic conductivity, chemical stability and thermal stability and a high transference number. These characteristics make it a promising material for integration in solid state batteries. Doping LLZO with certain elements like bismuth, gallium, aluminum and tantalum increases the ionic conductivity and reduces the stabilization temperature of the cubic phase. In this work a sol-gel method is used to synthesize Fe-doped LLZO (Li_7-3xFe_xLa₃Zr₂O₁₂), wherein a low calcination temperature of 700°C in air is used. XRD is used to characterize the cubic phase and presence of other impurity phases. SEM is used to determine the microstructure of the powder and the prepared pellets with different Fe stoichiometric content. Electrochemical impedance spectroscopy is used to determine the bulk conductivity of the Fe-doped LLZO pellets. The low synthesis and calcination temperature combined with the high ionic conductivity (and other favorable characteristics of the LLZO garnet) make this synthesis method and material highly attractive for lithium-ion solid state batteries. Future work will involve fabrication of polymer composite electrolytes with this material, looking for positive synergy of polymer and garnet characteristics.