Temperature-dependent solid electrolyte interphase reactions drive performance in lithium-mediated nitrogen reduction to ammonia

The solid electrolyte interphase (SEI) is a vital component to control mass transport and selectivity in the lithium-mediated reduction of N2 to NH3 (Li-N2R). Finding strategies that generate the optimal SEI, a complex network of organic and inorganic species, can potentially improve Li-N2R performance. Here, we unravel structure-property relationships of the SEI by correlating its composition with the NH3 Faradaic efficiency (FENH3). By modifying the reaction temperature, we alter electrolyte decomposition reactions and observe changes in the SEI that explain FENH3 trends between electrolyte solvents. We quantify a complex reaction environment at elevated temperatures where SEI formation is counteracted by etching reactions. This trade-off leads to temporal fluctuations of FENH3, but the maximal FENH3 can reach up to 40%, the highest value reported for batch cells at ambient pressure thus far. Our work underscores the potential of novel electrolytes that steer SEI selectivity and, ultimately, improve Li-N2R performance.