Microstructure–Interphase Co-Regulation Enables Stable Self-Supporting Al–Sn–Si Alloy Foil Anodes for Liquid and Sulfide-Based Lithium Batteries

Abstract Self-supporting alloy foil anodes provide a promising route toward cleaner and more resource-efficient lithium battery manufacturing by eliminating polymer binders, conductive additives, and additional current collectors. However, the practical use of Al-based alloy foils is still limited by unstable lithiation fronts, chemo-mechanical cracking, low initial Coulombic efficiency, and continuous interfacial side reactions. Herein, we report a microstructure–interphase co-regulation strategy for self-supporting AlSn28Si2 alloy foil anodes through low-temperature annealing and electrolyte-mediated mechanical prelithiation. Annealing at 150 °C for 30 min establishes an optimized microstructure–mechanics window consisting of refined Al grains, dispersed Sn/Si phases, and continuous grain/phase-boundary networks, resulting in a tensile strength of 268.1 MPa and an elongation of 6.9%. This structure suppresses crack initiation and uncontrolled lithiated-layer thickening while improving Li+ transport, with an average apparent diffusion coefficient of 8.08 × 10–12 cm2 s–1. Electrolyte-mediated mechanical prelithiation further increases the initial Coulombic efficiency from 51.8% to 84.1%, improves electrolyte wettability, and preconstructs a carbonate/fluoride-rich interphase. Benefiting from the coupled structural and interfacial stabilization, the optimized foil delivers stable cycling and rate performance in both liquid-electrolyte NCM811 full cells and sulfide-based all-solid-state batteries, including 4.08 mAh cm–2 after 600 cycles at 4.0 mA cm–2 and 1.1 mAh cm–2 at 10 mA cm–2. This work demonstrates a scalable metallurgical and interfacial engineering approach for developing high-performance self-supporting alloy foil anodes toward sustainable lithium battery production.