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

NASICON-type Li 1 . 5 Al 0 . 5 Ge 0 . 5 P 3 O 1 2 (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 LiBF 4 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% LiBF 4 has the highest ionic conductivity (3.21 × 10 − 4 S/cm), grain boundary impedance decreases from 162.2 Ω to 35.2 Ω , the relative density increases from 93.6% to 96.5%, and no impurity phase is observed in LAGP–0.5 wt% LiBF 4 . At the same ionic conductivity, the sintering temperature of LAGP without LiBF 4 and with a small amount of LiBF 4 decreases from 800 ∘ C to 700 ∘ C. The Li/LAGP-LiBF 4 /LiFePO 4 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.