Influence of LiBF4 sintering aid on the microstructure and conductivity of LATP solid electrolyte

To improve sintering performance, LiBF4, as a novel sintering aid, was added to a NASICON-type solid electrolyte LATP, which was synthesized by the sol-gel method. The microstructure, crystallinity and lithium-ion conductivity of the obtained LATP was measured by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectroscopy, MAS NMR and impedance spectroscopy (IS). Results indicate that during sintering, LiBF4 not only forms liquid phase to promote the growth of grains, but also forms a replacement solid solution with LATP. A small amount of boron and fluorine substitutes phosphorus and oxygen, thus entering the LATP lattice and forming a channel that is more suitable for Li-ion migration. The formation of the solid solution phase of LiBF4 and LATP also leads to the gradual disappearance of grain boundaries, which further promotes the improvement in ionic conductivity. The highest ionic conductivity of the LATP sintered pellet obtained with 3 wt% LiBF4 is 0.85 mScm−1.