Preparation and characterization of Ba-substituted Li1+xAlxGe2-x (PO4)3 (x=0.5) solid electrolyte

The substitution of Al in LAGP (Li1+xAlxGe2-x(PO4)(3)) by a divalent cation of Ba has been investigated in this study. The Ba-substituted glassy LAGP is prepared by a melt-quenching method, followed by crystallization from 750 to 850 degrees C for 8 h. The thermal gravity and differential thermal analysis (TG-DTA) and high temperature X-ray diffraction (HT-XRD) measurements reveal that the Ba substitution reduces the temperature of the onset of crystallization. The influence of the crystallization temperature on crystallinity, morphology and Li ion conductivity of LAGP is also studied. The formation of an impurity such as AlPO4 and BaGeP2O8 is observed in all samples and is promoted by an increase in the crystallization temperature. The Li ion conductivities of the Ba-substituted LAGP (LABGP) crystallized at 750, 800 and 850 degrees C are 4.7 x 10(-4), 2.9 x 10(-4), and 1.9 x 10(-4) S cm(-1), respectively. The LABGP crystallized at 750 degrees C contains more mobile Type II Li ions than others indicated by X-ray photoelectron spectroscopy (XPS), which contribute to improve the bulk Li ion conductivity, and as observed in the scanning electron microscope (SEM) image, it also contains more of the amorphous component, which reduces the grain-boundary resistance. As a result, the LABGP crystallized at 750 degrees C shows the highest Li ion conductivity. By suppressing the impurity formation, further improvements in the Li ion conductivity can be expected.