Effect of lithium-free flux B2O3 on the ion conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Abstract

Using solid electrolyte instead of liquid electrolyte is regarded as an important measure to solve the safety problems of lithium ion batteries, and has attracted wide attention of researchers. Among many solid electrolytes, Li1.3Al0.3Ti1.7(PO4)3 (LATP) is considered to be one of the most commercially available solid electrolytes for its high ionic conductivity. However, as a replacement substitute of for liquid electrolyte, the LATP solid electrolyte has an ionic transport property of LATP solid electrolyte that still needs to be improved. In this paper, LATP solid electrolyte used for lithium ion batteries is successfully prepared by solid reaction process, and the influences of different sintering temperatures and addition of flux B2O3 and or LiBO2 on the ionic conductivity of LATP solid electrolyte are discussed. The structures, element content, morphologies, and ionic conductivities of the sintered samples are investigated at room temperature by X-ray diffraction, energy dispersive spectrometer, electrochemical impedance spectrum and scanning electron microscopy. It is found that pure phase LATP ceramic solid electrolyte can be obtained at the sintering temperatures between 800 and 1000℃. And the ionic conductivities of the samples first increase first and then decrease with the increasing sintering temperatures increasing. The sample with a highest ionic conductivity of 4.1610-4 S/cm can be obtained at the a sintering temperature of 900℃. Further research shows that the ionic conductivities of the sintered samples can also be effectively improved by using B2O3 instead of LiBO2 as flux. Moreover, the ionic conductivities of the samples first increase first and then decrease with the increasing amount of the flux increasing. And the highest ionic conductivity of 1.6110-3 S/cm is obtained with the sampleby adding B2O3 with a mass fraction of 2% into the sample. The results indicate that the elevating of sintering temperature and the adding of flux B2O3 and or LiBO2 can both decreasing reducing the grain boundary impedances of the LATP samples, so as to thereby improve improving their ionic conductivities. However, when the sintering temperature is higher than 900℃ or the amount of flux B2O3 and or LiBO2 exceeds the mass percentage of 2%, the ionic conductivities of the LATP samples will drop. In addition, the ionic conductivities of the samples used using B2O3 as flux are higher than that those of the samples used LiBO2 as flux. These results also indicate that the increases of ionic conductivities of LATP samples with flux is are closely related to their densities density and compactness, and is irrespective of no matter whether or not the flux contains lithium ion.