Mechanistic Interrogation of Alloy Interlayers in Solid-State Batteries

Solid-state batteries employing lithium (Li) metal anodes have emerged as key enablers of a sustainable energy economy due to their high energy density and enhanced safety over their liquid electrolyte counterparts. However, achieving their full potential is limited by fundamental challenges arising from non-uniform reaction distribution and mechanical stresses at the Li metal-solid electrolyte interface, resulting in localized Li deposition, filament growth and subsequent short-circuit. Among the several strategies being developed to mitigate these interfacial instabilities, the use of a lithiophilic metal interlayer (e.g., Ag, Au) between the Li metal anode and the solid electrolyte has shown remarkable promise, exhibiting enhanced regulation of Li deposition-dissolution behavior and improved performance. However, the underlying mechanisms driving this improvement remain unexplored. In this work, we reveal the mechanistic interactions within alloy interlayers that enhance the stability of the Li metal anode. Through a mesoscale modeling framework that captures the coupled electro-chemo-mechanical interactions within the interlayer, we present the impact of thermodynamics, reaction kinetics, Li⁺ ion transport, Li diffusion, and mechanical stresses on Li deposition behavior and contact loss. Further, we analyze the role of volume expansion accompanying alloying and heterogeneities in reaction and mechanical stresses on the spatiotemporal evolution of the interlayer architecture. Overall, this work offers fundamental insights into interface stability with alloy interlayers for the design and development of robust solid-state batteries.