Imaging of nitrogen fixation at lithium solid electrolyte interphases via cryo-electron microscopy

Ammonia is an important industrial chemical and is also being discussed as a potential energy carrier. Electrifying ammonia synthesis could help to decarbonize the chemical industry, as the Haber–Bosch process contributes markedly to global carbon emissions. A lithium-mediated pathway is among the most promising ambient-condition electrochemical ammonia synthesis methods. However, the role of metallic lithium and its passivation layer, the solid electrolyte interphase (SEI), remains unresolved. Here we use cryogenic transmission electron microscopy as part of a multiscale approach to explore lithium reactivity and the SEI, discovering that the proton donor (for example, ethanol) governs lithium reactivity towards nitrogen fixation. Without ethanol, the SEI passivates lithium metal, rendering it inactive for nitrogen reduction. Ethanol disrupts this passivation layer, enabling continuous reactivity at the lithium surface. As a result, metallic lithium is consumed via reactions with nitrogen, proton donor and other electrolyte components. This reactivity across the SEI is vital to device-level performance of lithium-mediated ammonia synthesis.