Influence of LiBF4 sintering aid on the grain boundary and conductivity of LAGP electrolyte

NASICON-type Li1.5Al0.5Ge0.5P3O12(LAGP) is one of the most promising inorganic solid-state electrolytes (SSEs). However, its practical applications have been hindered due to the high grain boundary resistance and poor sintering performance. In this work, we introduce a novel LiBF4 sintering aid into LAGP to promote the growth of grains, decrease grain boundary resistance, and supplement the loss of lithium. The experimental results show that the ionic conductivity of LAGP-0.5 wt% LiBF4 has the highest ionic conductivity (3.21 x 10(-4)S/cm), grain boundary impedance decreases from 162.2 omega to 35.2 omega, the relative density increases from 93.6% to 96.5%, and no impurity phase is observed in LAGP-0.5 wt% LiBF4. At the same ionic conductivity, the sintering temperature of LAGP without LiBF4 and with a small amount of LiBF4 decreases from 800? to 700?. The Li/LAGP-LiBF4/LiFePO4 cell presents excellent cyclic stability (capacity retention of the discharge capacity is still 117.5 mAhg(-1) after 100 cycles) and a high initial discharge capacity of 164.2 mAhg(-1) at 0.2 C.