Unveiling Solid Electrolyte Interphase Dynamics in Electrochemical Lithium-Mediated Ammonia Synthesis via Operando Raman Spectroscopy

Lithium-mediated nitrogen reduction to ammonia (LiNRR) offers a sustainable pathway for ammonia synthesis under ambient conditions, but the role of the solid electrolyte interphase (SEI) remains unclear. Here, operando Raman spectroscopy yielding realistic ammonia Faradaic efficiencies in THF-based LiClO4 and LiFSI electrolytes revealed how SEI composition and dynamics drive ammonia synthesis. By systematically probing the interaction between N2, ethanol and electroplated Li, we found that ethanol, beyond acting as a proton donor, actively reshapes the SEI via lithium ethoxide formation, thereby enabling N2 activation. Tuning electrolyte composition led to high LiNRR performance of up to 16% Faradaic efficiency, 5 nmol s-1 cm-2 rate and a low overpotential of -0.4 VLi+/Li in 1.0 M LiFSI. High activity correlated with SEIs enriched in lithium alkoxides and LiOH, which enhances the reactivity of the Li surface toward N2 and H+. Our results highlight the SEI as a key regulator of N2, H+ and Li+ transport and offer design principles for efficient ammonia electrosynthesis.