High‐Conductivity Argyrodite Electrolyte with Self‐Passivating Stability for Single‐Electrolyte All‐Solid‐State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) are promising candidates for next-generation energy storage due to their enhanced safety and energy density. Among solid-state electrolytes (SSEs), argyrodite-type Li₆PS₅X compounds offer economic advantages but suffer from limited ionic conductivity and electrochemical stability. In this study, we design a novel SSE, Li_5.5P_0.94Ta_0.06S_4.5Cl_0.75Br_0.75, featuring dual halide (Cl^-/Br^-) occupation and Ta⁵⁺ substitution to enhance conductivity and interfacial compatibility. The resulting SSE exhibits a high ionic conductivity of 12 mS cm^-1 at room temperature. Inspired by Al corrosion passivation, it forms in situ self-passivating interfacial layers, ensuring stability against both lithium metal anodes and high-voltage cathodes. Batteries incorporating this electrolyte achieved 100% capacity retention over 200 cycles at 0.2C, and over 81% retention after 1200 cycles at 0.5C. Under high-loading (30 mg cm^-2) and N/P = 1.8 conditions, 81% capacity was maintained after 150 cycles. A 10 × 6 cm² pouch cell retained 96.4% of its capacity after 200 cycles. This work offers a viable route toward high-performance, scalable ASSLBs using a single-passivating electrolyte.