Insights on the Properties of the O-Doped Argyrodite Sulfide Solid Electrolytes (Li₆PS_5–<i>x</i>ClO_<i>x</i>, <i>x</i>=0–1)

Abstract

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 (Li₆PS_5-<i>x</i>ClO_<i>x</i>, <i>x</i> = 0-1). It is found that Li₆PS_4.75ClO_0.25 (LPSCO_0.25) with <i>x</i> = 0.25 and cubic phase (<i>F</i>4̅3 <i>m</i>) 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/LPSCO_0.25/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/LPSCO_0.25/Li-In cell is assembled using bare LiNi_0.83Co_0.06Mn_0.11O₂ 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 Li₆PS_5-<i>x</i>ClO_<i>x</i> 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 LPSCO_0.25, further confirming the above conclusion.