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

Abstract

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 75Li2S·(25-x)P2S5·xP2O5 (mol%) solid state electrolytes are prepared by optimized mechanical milling technique and subsequent heat-treatment process. The electrolyte substituted with 1 mol% P2O5 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 75Li2S·24P2S5·1P2O5 electrolyte exhibits good electrochemical stability and compatibility with the metallic lithium electrode. The all-solid-state cell with a structure of LiCoO2/75Li2S·24P2S5·1P2O5/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 75Li2S·25P2S5 as electrolyte.