At present, sulfide-based solid electrolytes have attracted considerable attention, especially argyrodite-type solid electrolyte, Li6MS5X (X=Cl, Br, I), due to its appropriate mechanical strength and high ionic conductivity (>10-3 S/cm). However, it still falls short of liquid electrolytes in terms of ionic conductivity and has the fatal drawback of being unstable to moist air. First, we prepare SeS₂ doped Li6PS5Cl through high-energy ball milling followed by heat treatment. We also confirm the structural properties using powder X-ray diffraction (XRD) and Raman analyses. Next, we perform surface morphology and elemental analysis using a field emission scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscope (EDS). The synthesized Li6.03P0.97Se0.03S5Cl electrolyte shows a higher ionic conductivity of 5.4 mS/cm and a lower activation energy of 26.5 kJ/mol compared to pristine Li6PS5Cl (4.4 mS/cm, 27.2 kJ/mol) at 20 ℃, and it also shows good stability against Li metal. The optimized electrolyte shows a higher initial discharge capacity of 175 mAh/g and coulombic efficiency of 67.6%. Interestingly, Li6.03P0.97Se0.03S5Cl showed 61.5% of the 1 C rate capacity compared to that at the 0.05 C rate, which was significantly improved compared to the corresponding value of the pristine. Finally, to measure the air stability properties, the H₂S generation amount test and EIS test were both performed before and after exposure to air and Li6.03P0.97Se0.03S5Cl shows a high ionic conductivity of 3.06 mS/cm after 30 min dry air exposure.
Second, we prepare the air stability and electrochemical performance of the solid electrolyte were improved by introducing a method to improve the performance of the solid electrolyte by adding excess iodine based on a thioantimonate-based argyrodite solid electrolyte with excellent air stability. I-rich glass-ceramic argyrodite Li6-xSbS5-xIx was prepared through high-energy ball milling. The structural properties were confirmed using powder X-ray diffraction (XRD). The synthesized Li5.6SbS4.6I1.4 electrolyte showed a higher ionic conductivity of 0.7 mS/cm and a lower activation energy of 0.32 eV compared to pristine Li6SbS5I (0.2 mS/cm, 0.33 eV) at 25 ℃. In addition, the high lithium compatibility of the Li5.6SbS4.6I1.4 solid electrolyte was confirmed through DC cycling and cyclic voltammetry, and it showed a high ion conductivity retention rate of 61% after exposure to the atmosphere for 30 minutes. Finally, the optimized cell with Li6PS5Cl-Li5.6SbS4.6I1.4 solid electrolyte showed a higher initial discharge capacity of 154 mAh/g and coulombic efficiency of 70 %. In particular, it was confirmed that the performance at high C-rate was greatly improved compared to the cell made with Li6PS5Cl.