Chemo‐Mechanical Failure and Reinforcement of Solid Electrolyte Films for Practical All‐Solid‐State Li Metal Pouch Cells

All-solid-state Li metal batteries (ASLMBs) are the key to achieving high energy densities; however, studies on practically relevant pouch-type cells remain scarce. A critical challenge lies in integrating thin solid electrolyte films, particularly under the high pressures required for cell assembly, which has been largely overlooked. Here, we reveal the inherent incompatibility of conventional sulfide solid electrolyte films with Li metal during pouch cell assembly. To address this challenge, we introduce a simple yet effective post-engineering strategy that modifies the chemical interactions between Li₆PS₅Cl and nitrile butadiene rubber binders, significantly enhancing the mechanical robustness and Li metal compatibility, even under 450 MPa isostatic pressing. Complementary experimental analyses and finite element method simulations identify the underlying enhancement mechanism as the improvement of mechanical properties, which increases the interfacial friction. Leveraging these advancements, we successfully assemble LiNi_0.70Co_0.15Mn||Li ASLMB pouch cells without any interlayers through single-step pressurization, achieving remarkable performance at 3 MPa, with 400-cycle stability at 60°C and reliable operation at 30°C. Finally, we demonstrate a proof-of-concept bipolar-stacked ASLMB pouch cell, showcasing its scalability and practicality. These findings establish a new benchmark for ASLMBs and provide key design principles for advancing practical high-energy all-solid-state technologies.