In Situ Raman Spectroscopy Reveals the Dynamic Evolution and Ethanol Dependence of SEI Structure in Li-Mediated N ₂ Reduction Reaction

The lithium-mediated nitrogen reduction reaction (Li-NRR) provides a promising strategy toward green NH 3 synthesis. While the proton donors are essential for Li-NRR, their role in modulating the chemistry and structure of the solid-electrolyte interphase (SEI) is still poorly understood. Here, we utilize in situ Raman spectroscopy, combined with X-ray and SEM characterization, to decipher the Li-NRR process and solid electrolyte interphase (SEI) dynamics under operating conditions. It was revealed that the SEI evolves from solvent-derived organic composition to lithium salt-involved inorganic nature as the reaction proceeds. Furthermore, ethanol was found to critically govern the chemical composition and physical morphology of SEI by tuning the content of LiF and LiBO 2 compounds. This inorganic identity of SEI in turn produces a thin, uniform, and compact electrode surface, which regulates the mass transport of N 2, Li +, and proton donor to promote the Li-NRR performance. These results establish a direct and tunable link among ethanol content, SEI structure, and Li-NRR performance and envision the tailored engineering to achieve device-scale NH 3 production.