Fig. 3. Formation and evolution of SEIs in the dual-salt electrolyte revealed by DS-PERS.

a–c E–t curve of the galvanostatic polarization (denoted as the G route) of Li plating on Cu (a). In-situ Raman spectra recorded during the formation and evolution of the SEI under the G route (b). Peaks marked by asterisks are from the electrolyte. Schematics of the structure and chemistry of the SEI formed under the G route (c). d, e j–t and E–t curves of electrochemically engineered potentiostatic-galvanostatic polarization (denoted as the P-G route) of Li plating on Cu (d). In-situ Raman spectra recorded during the formation and evolution of the SEI under the P-G route (e). Schematics of the structure and chemistry of the SEI formed under the P-G route (f). g, h Normalized Raman peak area of bands associated with B–O and carbonate species in sequentially formed Li-SEI (g) and directly formed Li-SEI (h). i, j Percentages of specified components in the sequentially formed Li-SEI (i) and directly formed Li-SEI (j), calculated from the XPS spectra.