Interfacial Stability between Li-Metal/Si Composite Anode and Sulfide Solid Electrolytes in Direct Die-Pressed and Isostatically Pressed All-Solid-State Batteries

All-solid-state batteries (ASSBs) employing Si–Li composite anodes are promising candidates for achieving high energy density and scalable practical applications. Incorporating metallic Li into Si anodes as a compensation source offers a promising approach to compensate for irreversible Li consumption. Nevertheless, the introduced metallic Li must be carefully regulated to provide sufficient Li compensation for the Si anode while preventing excessive reactions with Li5.5PS4.5Cl1.5 (LPSC). Achieving this delicate balance is therefore essential for constructing stable LPSC/Li@Si interfaces. Herein, we systematically investigate the interfacial stability of Li-metal-prelithiated Si anodes in sulfide-based ASSBs under both direct die-pressing and isostatic pressing conditions. Using NCM811|LPSC|Li@Si cells as a model system, we identify the appropriate Li thicknesses for different cell configurations and demonstrate that stable cycling critically depends on directing the redistributed metallic Li into the porous Si electrode rather than into the sulfide solid electrolyte layer. Such interfacial regulation effectively suppresses the continuous decomposition of LPSC and mitigates the growth of interfacial resistance. Benefiting from the optimized prelithiation and pressing protocol, the application of Li-metal-prelithiated Si anodes was successfully extended from direct die-pressed mold-type full cells (mold cells) to isostatically pressed pouch-type full cells, highlighting their potential for practical high-energy ASSBs.