(322l) Imaging of Nitrogen Fixation at Lithium Solid Electrolyte Interphases Via Cryo-Electron Microscopy

Ammonia is among the most important commodity chemicals and being discussed as a potential energy carrier. Haber–Bosch process contributes significantly to global carbon emissions, however, motivating the development of alternative sustainable methodology for ammonia synthesis. An electrifying lithium-mediated ammonia synthesis (LiMEAS) is one of promising ways to decarbonize the chemical industry. This process takes advantage of the facile and thermodynamically favorable reaction between dinitrogen and lithium (Li) metal, generating ammonia by electrodepositing Li from organic electrolyte. Considering metallic Li is extremely reactive, its reactions with the liquid electrolyte to form the solid electrolyte interphase (SEI) usually concurrently happen together with its electrodeposition. The roles of metallic Li and its passivation layer, the SEI, remain unresolved during the LiMEAS reactions. We use cryo-EM as part of a multiscale approach to explore Li reactivity and the SEI, discovering that the proton donor (e.g., ethanol) emerges as the key determinant of surface chemistry towards nitrogen in LiMEAS. In the absence of ethanol, the working electrode surface accumulates metallic Li in the form of filamentary deposits with a passivating SEI that prevents nitrogen reduction on Li surface (Figure 1a-c). With ethanol disrupting the SEI layer, metallic Li reacts continuously with electrolyte and nitrogen, leaving behind a mosaic-structured SEI-like material with amorphous phases dominated by ethanol breakdown products (Figure 1d-f). Together, our results revise current understanding of surface phenomena in LiMEAS and demonstrate that the Li SEI can be an essential reactive interphase. Rather than a passivating SEI preserving the productivity of a metallic Li deposit, the SEI in LiMEAS must allow Li to react in a series of thermochemical reactions.

Figure 1 a-b) cryo-EM image and c) schematic of Li metal with SEI layer without proton donor, d-f) analogous images to a-c but collected with proton donor, ethanol.