Interfacial Li+ Diffusion in Li2O SEI as a Driver of Lithium Whisker Growth

Lithium metal is a highly attractive negative electrode for next-generation lithium batteries, but its practical use is still limited by filamentary growth, which is increasingly linked to how lithium ions and atoms move through and along the solid–electrolyte interphase (SEI). In this work, we use first-principles calculations and electrostatic modeling to clarify how native Li defects in Li2O, a representative inorganic SEI component, and at the Li/Li2O interface contribute to ionic transport. We show that in ideal bulk Li2O lithium migration is almost entirely vacancy-mediated and intrinsically very slow, implying that microstructure and interfaces, rather than the bulk oxide, provides Li+ transport in real SEI layers. At the Li/Li2O interface, however, lattice softening and image-charge effects strongly stabilize charged defects in the nearest oxide layers, dramatically increasing their concentration without significantly changing migration barriers. As a result, a nanometer-thin interfacial region can act as a fast lateral transport channel that redistributes lithium along the metal surface and can efficiently feed the bases of growing whiskers, even when the SEI remains a good through-plane blocking layer. This interfacial-transport picture helps rationalize diverse experimental observations of lithium whisker formation and highlights interfacial defect engineering in SEI-forming oxides as a powerful design lever. The insights provide clear guidelines for tailoring SEI composition, thickness, crystallinity, and dopant chemistry to steer lithium flux, mitigate filament growth, and enable safer, longer-lived lithium-metal electrodes and related architectures in advanced lithium and energy storage systems.