Alloy Anodes: Mechanistic Regulation of Reaction and Transport at Solid–Solid Interfaces

Lithium alloys are promising alternatives to Li metal anodes for solid-state batteries, potentially mitigating filament formation while retaining high specific capacities. However, the mechanisms underlying alloying and their influence on interface stability remain poorly understood. In this work, we demonstrate how electro-chemo-mechanical and transport interactions in alloy anodes affect electrodeposition dynamics and solid–solid interface stability. Despite thermodynamic favorability for alloying, we reveal that kinetic limitations from mechanical stresses and restricted Li diffusion can induce Li plating at the alloy anode/solid electrolyte interface. The alloying-to-plating transition is governed by mechanics-driven reaction limitations, primarily dictated by the alloy yield strength. We also identify distinct mechanistic regimes limiting anode utilization during plating onset, determined by the Li diffusivity of the alloy. Our findings establish yield strength and diffusivity as critical design criteria and underscore the need for physics-informed co-optimization of material properties and operating conditions to enable stable alloy anodes in solid-state batteries.