Musah Abdulai1 Kamil Burak Dermenci1 Servet Turan1

1, Materials Science and Engineering, Eskisehir Technical University, Eskisehir, , Turkey

Solid-state electrolytes are attracting more interest in battery technology due to the recent safety issue brought by the liquid type electrolytes such as flammability,toxicity etc. In recent years,lithium lanthanum zirconium(LLZO) is one of the solid electrolytes which has received attention due to the presence of wide chemical stability window, stability with lithium metal and high ionic conductivity at room temperature.The LLZO has two crystal phase,the stable phase which is the tetragonal and the cubic phase, the unstable phase. The attainment of the cubic phase which has the highest ionic conductivity is challenging as it required higher sintering temperature and dopants.The stabilization of garnet-type LLZO solid-state electrolyte in a cubic phase with appropriate dopants has become essential since they reduced the sintering temperature, sintering time and improved lithium-ion conductivity. However, not much data has been reported regarding the role of Lanthanide series elements at the La-site on cubic phase stabilization of LLZO. In the present work, a solid-state electrolyte for the composition Li7La3-xMxZr2O12 (M=Sm3+, Dy3+,Er3+ Yb3+; x=0.1-0.8) has been synthesized through the solid-state method. High-quality oxide powders were used. A stoichiometric weighed quantities of the starting powders were ground and calcined at 1000oC for 10 hours. The calcined powders were pressed into pellets and cold isostatically pressed at 265 MPa. They are sintered in air at 1200oC for 12-18 H using powder bed method. A critical investigation carried out by X-ray powder diffraction and refinement analysis revealed the synthesis of pure cubic LLZO phase. The solubility content of selected ions decreased with smaller size ions. The densities measured by using the famous Archimedes method increases as the ionic content in the garnet framework increased. Pellets having relative densities ranging from 73g/cm3 to 98g/cm3 out of the theoretical density of LLZO (5.1 g/cm3) were produced. The lattice parameter determined by both the analytical and the refinement technique obey the so-called Vegard’s law. However, the Yb3+ exhibits a negative slope due to the shrinkage that occurred. The SEM images indicate the reduction of porous microstructure with an increase in ionic contents which is consistent with the measured density values. EDS analysis confirmed the presence of the mentioned ions at this content. Lastly,the smaller ionic radius ions were observed to produced higher ionic conductivity of the garnet-type solid electrolyte.