Flexible Sulfide Electrolyte Thin Membrane with Ultrahigh Ionic Conductivity for All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) employing Li-metal anode, sulfide solid electrolyte (SE) can deliver high energy density with high safety. The thick SE separator and its low ionic conductivity are two major challenges. Herein, a 30 μm sulfide SE membrane with ultrahigh room temperature conductivity of 8.4 mS cm^-1 is realized by mechanized manufacturing technologies using highly conductive Li_5.4PS_4.4Cl_1.6 SE powder. Moreover, a 400 nm magnetron sputtered Al₂O₃ interlayer is introduced into the SE/Li interface to improve the anodic stability, which suppresses the short circuit in Li/Li symmetric cells. Combining these merits, ASSLBs with LiNi_0.5Co_0.2Mn_0.3O₂ as the cathode exhibit a stable cyclic performance, delivering a discharge specific capacity of 135.3 mAh g^-1 (1.4 mAh cm^-2) with a retention of 80.2% after 150 cycles and an average Coulombic efficiency over 99.5%. The high ionic conductivity SE membrane and interface design principle show promising feasible strategies for practical high performance ASSLBs.