Unveiling solid electrolyte interphase dynamics in electrochemical lithium-mediated ammonia synthesis via operando Raman spectroscopy

During electrochemical lithium-mediated nitrogen reduction to ammonia (LiNRR), the formation and function of the solid electrolyte interphase (SEI) remain poorly understood. Here operando Raman spectroscopy yielding realistic ammonia Faradaic efficiencies in tetrahydrofuran-based lithium perchlorate (LiClO4) and lithium bis(fluorosulfonyl)imide (LiFSI) electrolytes reveals how SEI composition and dynamics govern ammonia synthesis. By systematically probing the interaction between N2, ethanol and electroplated Li, we find that ethanol, beyond acting as a proton donor, actively reshapes the SEI via lithium ethoxide formation, thereby enabling N2 activation. Tuning the electrolyte composition shows that higher conversion to NH3 correlated with SEIs enriched in lithium alkoxides and LiOH, which enhanced the reactivity of the Li surface towards N2 and H+. Our results highlight the SEI as a key regulator of N2, H+ and Li+, tunable by electrolyte additives, providing design principles for efficient ammonia electrosynthesis. Understanding the role of solid electrolyte interphase (SEI) under reaction conditions is crucial to improving the efficiency of electrochemical lithium-mediated N2 reduction. Here, operando Raman spectroscopy is used to investigate the effect of electrolyte, proton donor and gas environments on SEI composition and its resultant performance and stability.