This work presents a dimethoxyethane (DME) / sodium bis(fluorosulfonyl)imide (NaFSI) (2/1 (n/n)) electrolyte that forms a stable and resilient passivation layer on sodium metal, as indicated by highly reversible sodium plating/stripping. Further investigation of the passivation layers by post-mortem FTIR and 1H-NMR analysis reveals that conventional organic carbonate based electrolytes decompose to organic salts such as sodium ethyl dicarbonate. In contrast, the DME/NaFSI electrolyte forms ethereal and alkoxide species as well as inorganic salts derived from the FSI anion. These compounds ensure sodium metal passivation and thereby enable more reliable and efficient testing in Na-ion half cells.
 Iermakova, D. I.; Dugas, R.; Palacin, M.R.; Ponrouch, A. J. Electrochem. Soc. 2015, 162, A7060-A7066