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

摘要

Lithium garnet-like structure with the substitution of Zr4+ sites by the same value of Ge4+ in the Li7La3Zr2O12 (LLZO) has been synthesized by a solid state reaction. The results indicate that doping Ge4+ in the LLZO was able to reduce the sintering temperature as well as increase the density of the pellets. The prepared samples Li7La3Zr2-xGexO12 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 degrees C, and the high ionic conductivity can be obtained with 4.78 x 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 Li7La3Zr2-xGexO12 possessed a wide electrochemical window. A full cell containing the Li7La3Zr2-xGexO12 electrolyte was assembled to test the electrical performance, which demonstrates that the first discharge capacity can reach up to 139.1 mA g 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.