<i>In Situ</i> Halide/Alloy Coating Stabilizes the Solid-State Battery Lithium Anode Interface

All-solid-state lithium-ion batteries (ASSLIBs) based on sulfide solid-state electrolytes (SSEs) are extensively used due to their high energy density. However, the interface instability between sulfide SSEs and lithium (Li) metal often results in the uncontrolled growth of Li dendrite, causing battery failure. Here, a protective layer constituted by a carbon–iodine–silver (C-I2-Ag) composite was introduced between the sulfide SSEs and Li metal, establishing a stable Li/SSEs interface. Carbon (C) can firmly confine iodine (I2) by forming C–I bonds and acting as a conductive carrier. In situ-formed lithium iodide (LiI) presents inherent stability with Li and SSEs to overcome the interfacial parasitic reactions. The alloy between Li and Ag further eliminates the Li dendrites to ensure the long durability of ASSLIBs. The ASSLIBs incorporating the protective layer can operate reliably at 0.15 mA cm–2 for over 1500 h at 25 °C without encountering a short circuit. A symmetric battery’s critical current density can be as high as 4.6 mA cm–2. In addition, compared with the Li metal battery lacking an interfacial layer, after 110 cycles, the capacity retention rate of the ASSLIBs containing C-I2-Ag was as high as 93.55%. This advancement paves the way for the continued progress of ASSLIBs with high energy density.