In Situ Raman Spectroscopy Reveals the Dynamic Evolution and Ethanol Dependence of SEI Structure in Li-Mediated N2 Reduction Reaction.

The lithium-mediated nitrogen reduction reaction (Li-NRR) provides a promising strategy toward green NH3 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 LiBO2 compounds. This inorganic identity of SEI in turn produces a thin, uniform, and compact electrode surface, which regulates the mass transport of N2, 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 NH3 production.