Effects of B2O3 on microstructure and ionic conductivity of Li6.5La3Zr1.5Nb0.5O12 solid electrolyte

Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZN) garnet-type structure was synthesized at low temperature with B₂O₃ addition by solid state reaction method. The effects of B₂O₃ content on the formation, microstructure, ionic conductivity and activation energy of the LLZN solid electrolytes have been investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and alternate current (AC) impedance spectroscopy. The cubic LLZN phase was obtained after calcining at 850 °C for 6 h and no phase evolution was observed after sintering at 1100 °C for 6 h. The relative density and lithium ion conductivity increased first and then decreased with increasing B₂O₃ content, reaching the maximum value of 92.4% and 1.86×10⁻⁴ S cm⁻¹ respectively in the sample with 1.4 wt% B₂O₃. By contrast, the activation energy reached a minimum value of ~31.5 kJ mol⁻¹.