Structure and ionic conductivity of Li7La3Zr2−xGexO12 garnet-like solid electrolyte for all solid state lithium ion batteries

Abstract Lithium garnet-like structure with the substitution of Zr 4+ sites by the same value of Ge 4+ in the Li 7 La 3 Zr 2 O 12 (LLZO) has been synthesized by a solid state reaction. The results indicate that doping Ge 4+ in the LLZO was able to reduce the sintering temperature as well as increase the density of the pellets. The prepared samples Li 7 La 3 Zr 2−x Ge x O 12 with cubic garnet like structure were characterized by X-ray diffraction and Raman spectra. The lithium ionic conductivity of all components was characterized by AC impendence at 20 °C, and the high ionic conductivity can be obtained with 4.78 × 10 −4  S/cm, while a low activation energy was only about 0.29 eV in the temperature range from 253 to 213 K. The solid electrolyte of Li 7 La 3 Zr 2−x Ge x O 12 possessed a wide electrochemical window. A full cell containing the Li 7 La 3 Zr 1.7 Ge 0.3 O 12 electrolyte was assembled to test the electrical performance, which demonstrates that the first discharge capacity can reach up to 139.1 mA g −1 at 0.1 C and the discharge capacity remains at 140.6 mA g −1 after 20 cycles. These excellent performances indicate that Ge doping LLZO could be a promising electrolyte candidate for all solid state Li ion batteries.