Insights on the Properties of the O-Doped Argyrodite Sulfide Solid Electrolytes (Li6PS5–xClOx, x=0–1)
Argyrodite sulfide solid electrolytes, such as Li6PS5Cl (LPSC), have received much attention due to their high ionic conductivity (>1 mS cm–1) and success in all-solid-state batteries (long cycle performance, high energy density, etc.). Numerous efforts are spent on modifying the properties of the electrolyte itself. Here, we combine first-principles calculations with experiments to investigate O-doped argyrodite sulfide solid electrolytes (Li6PS5–xClOx,x = 0–1). It is found that Li6PS4.75ClO0.25 (LPSCO0.25) with x = 0.25 and cubic phase (F4̅3 m) shows the highest ion conductivity of 4.7 mS cm–1 (cold-pressed), higher than that of undoped Li6PS5Cl (4.2 mS cm–1). The bare LiCoO2/LPSCO0.25/Li–In all-solid-state battery exhibits an initial capacity of 131 mA h g–1 at 0.1 C and satisfactory cycling stability with 86% capacity retention after 250 cycles to the 4th cycle at 0.3 C under 25 °C. In addition, the NCM811/LPSCO0.25/Li–In cell is assembled using bare LiNi0.83Co0.06Mn0.11O2 cathode and shows an initial discharge capacity of 181 mA h g–1 at 0.1 C and 160 mA h g–1 at 0.3 C. The doping of oxygen-forming Li6PS5–xClOx also improves the stability to Li metal, proven by cyclic voltammetry and powder X-ray diffraction tests. The calculation results for the band structure reveals that LPSC has the lowest unoccupied molecular orbital than LPSCO0.25, further confirming the above conclusion.
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