Thin, Highly Ionic Conductive, and Mechanically Robust Frame-Based Solid Electrolyte Membrane for All-Solid-State Li Batteries

A thin but robust solid electrolyte layer is crucial for realizing the theoretical energy density of all-solid-state batteries (ASSBs) beyond state-of-the-art Li-ion batteries (LIBs). This study proposes a simple but practical strategy for fabricating thin solid electrolyte membranes using 5-mu m perforated polyethylene separators with 35% open areas as the supporting component, which ensures mechanical robustness for commercial-level cell assembly. The thickness of this frame-based solid electrolyte (f-SE) membrane can be reduced to approximate to 45 mu m, even after coating the Li6PS5Cl (LPSCl) solid electrolyte composite. Despite a slightly lower ionic conductivity compared to that of thick LPSCl pellets, the f-SE membranes show high conductance and low overpotential in Li||Li symmetric cells. Their incorporation into LiNi0.7Co0.15Mn0.15O2 full cells increases the reversible capacity and rate capability compared to those of cells with conventional LPSCl pellets. The f-SE membrane cells exhibit excellent cycling stability over 250 cycles, while maintaining high-capacity retention and Coulombic efficiency. Notably, the f-SE membranes significantly increase the energy density of ASSBs (314 Wh kg-1), exceeding the values reported for sulfide-based cells. These results highlight the crucial role of f-SE membranes in improving the mechanical properties and energy density of ASSBs, thereby contributing to the development of next-generation Li battery technologies. A strategy for design thin and robust solid electrolyte (SE) membranes is proposed by simply introducing a perforated polyethylene separator as supporting frame. The frame-based SE membranes exhibit excellent mechanical strength properties and high ionic conductance, result in high-capacity retention and stable cycling in NCM||Li cells with an extreme mono-cell-level energy density of 314 Wh kg-1.image