Lanthanide doping of Li7La3-xMxZr2O12 (M=Sm, Dy, Er, Yb; x=0.1–1.0) and dopant size effect on the electrochemical properties

Abstract Lithium-ion batteries, as one of the energy storage devices, has attracted much attention due to its remarkable characteristics. However, they pose safety challenges because of their liquid electrolytes. Solid electrolytes are one of the key candidates to tackle the safety issues in Li-ion batteries. As a solid electrolyte, garnet-type Li7La3Zr2O12 is a promising candidate with its high stability against lithium metal and wide electrochemical window among its counterparts. But, the ionic conductivity is yet to be compared with liquid electrolytes. Hence, doping is still the common strategy to adjust the ionic conductivities. Despite the fact that doping with various elements is well-documented, Lanthanide group element doping is not thoroughly investigated. This research is to study the synthesis of garnet-type Li7La3-xMxZr2O12 (M = Sm, Dy, Er, Yb; x = 0.0–1.0) novel compositions to enlighten the effect of lanthanide group element doping as a function of ionic radius. Results showed that increasing dopant ionic radius improves densification, diminishes Li-ion conduction and, except Yb case, expands the lattice. However, impurity phases formed when the solubility limit is reached, has overall a positive impact on Li-ion conduction. The highest ionic conductivity (0.15 mS/cm) and lowest activation energy (0.18 eV) without impurity phases were obtained from Yb doped LLZO. It was also found that the presence of LiDyO2 improves the ionic conductivity to 0.16 mS/cm.