Lithium Alloying Strategies for Anode/Solid‐State Electrolyte Interface Engineering in Solid‐State Lithium Metal Batteries

All‐solid‐state lithium metal batteries (ASSLMBs) are considered a potential next‐generation system with enhanced safety and high energy density. Nonetheless, the practical application is greatly limited by the multiple interface failures between the anode and solid‐state electrolyte, including poor solid–solid contact, permanent interface‐side reactions, controllable lithium (Li) dendrite growth, and accumulated internal stress. Alloying modification strategy provides a versatile avenue for resolving these interface failures. This review summarizes recent progresses on the interface‐directed alloying strategy from three perspectives. The fully alloy anode takes advantage of the corresponding thermodynamic and mechanical properties to effectively suppress the interface failures. The composite embedded alloy framework approach decouples the structural support from Li storage, by 3D scaffolds confining a homogeneous lithium‐ion (Li ⁺ ) flow and keeping high capacity. Artificial mixed‐conducting interphases actively control charge transfer by a gradient structure for electronic conduction and ionic conduction, suppressing electrolyte decomposition. By analyzing design principles and performance limits of those strategies, this review gives an insightful basis for rational interface design. Finally, depending on current limitations, this review presents future prospects, aiming at giving a practical instruction for the rational design of stable interfaces and accelerating the advancement of ASSLMBs from laboratory research into practical applications.