Facile synthesis of lithium argyrodite Li5.5PS4.5Br1.5 with high ionic conductivity for all-solid-state batteries

Bromine-rich lithium argyrodite electrolytes with high ionic conductivity and low cost are promising for the replacement of flammable liquid electrolytes and separators in lithium-ion batteries. However, the synthesis process of argyrodite electrolytes is usually complex and time-consuming. We use a facile solid-state reaction method to obtain a highly Li-ion conductive Li5.5PS4.5Br1.5 (LPSB). The influence of annealing temperature on the phase and ionic conductivity of the LPSB was investigated for the first time. High ionic conductivity of 5.21 × 10−3 S cm−1 at room temperature for the LPSB with minor LiBr impurity was achieved by direct annealing at 430°C for 8 h. The In/InLi | LPSB | LiCoO2@ LiNb0.5Ta0.5O3 (LCO(coated))-LPSB cell with 8.53 mg cm−2 LCO loading shows a discharge capacity of 102 mAh g−1 with high-capacity retention of 93% after 70 cycles at 0.5 mA cm−2 at 30°C.