Lithium Superionic Conducting Oxysulfide Solid Electrolyte with Excellent Stability against Lithium Metal for All-Solid-State Cells

For the high-energy battery using Li metal as a negative electrode, the electrolyte is one of the most critical factors that significantly affects the cell performance. Herein, new 75Li 2 S·(25- x )P 2 S 5 · x P 2 O 5 (mol%) solid state electrolytes are prepared by optimized mechanical milling technique and subsequent heat-treatment process. The electrolyte substituted with 1 mol% P 2 O 5 presents the highest conductivity of 8 × 10 −4 S cm −1 at room temperature, which increases up to 56% compared to that of the pristine sample. The enhanced conductivity could be attributed to the decrease of the activation energy for Li + -ion diffusion. The as-prepared 75Li 2 S·24P 2 S 5 ·1P 2 O 5 electrolyte exhibits good electrochemical stability and compatibility with the metallic lithium electrode. The all-solid-state cell with a structure of LiCoO 2 /75Li 2 S·24P 2 S 5 ·1P 2 O 5 /Li shows a discharge capacity of 109 mAh g −1 at 0.1 C and high capacity retention 85.2% after 30 cycles at 25°C, which are better than these of the cell use the 75Li 2 S·25P 2 S 5 as electrolyte.