Mechanical integrity of the solid-electrolyte interphase and its role in regulating lithium deposition morphology

The performance and safety of lithium (Li) metal batteries are critically influenced by the properties of the solid-electrolyte interphase (SEI), which governs the morphology of Li deposition on electrodes. Despite extensive studies, the dynamic coupling between the mechanical integrity of SEIs and the evolution of Li deposition morphology remains poorly understood. In this study, we develop a coupled electro-chemo-mechanical framework that explicitly accounts for SEI damage and regeneration, along with their feedback regulation on the kinetics of Li deposition. Based on this framework, we build a numerical model to investigate the interplay between ion transport, charge transfer, stress accumulation, mechanical failure, and subsequent healing of the SEI during Li deposition. Numerical results reveal that the damaged SEI can act as a nucleation site for dendritic Li growth due to enhanced local ionic conductivity and thus accelerated local deposition, while SEI regeneration can restore interfacial integrity and suppress morphological nonuniformity. Key parameters, including SEI fracture strength, regeneration rate (governed by solvent diffusivity), and damage rate (governed by applied current density), are systematically varied to construct a phase map of morphology evolution, elucidating the competitive dynamics between SEI damage and regeneration. The modeling results are supported by experimental characterizations using atomic force microscopy (AFM)-based nanoindentation and post-mortem scanning electron microscopy (SEM), which confirm that mechanically robust SEIs correlate with uniform Li deposition and suppressed Li dendrite formation. This study highlights the critical role of SEI mechanical resilience and dynamic evolution in governing Li morphology, and provides both theoretical understanding and practical design principles for developing advanced electrolytes and artificial SEIs to enable safe, long-life Li metal batteries.