Fig. 2. Characterizations of SEI formed in the 1 M LiTFSI in DME-DOL using DS-PERS.

a, b In-situ Raman spectra showing the sequential formation and evolution of SEIs on the nanostructured Cu substrate (a) and the Cu-SHINs substrates (b) before and after Li deposition. Raman spectra of the bulk electrolyte are displayed for comparison. Peaks marked by asterisks are from the electrolyte. c Schematic comparison of the depth-fixed strategy based on LSPs of Cu alone and the depth-sensitive strategy based on synergetic LSPs of integrated Cu-SHINs for in-situ probing the formation and restructuring of SEI. By the DS-PERS, it is revealed that the primary Cu-SEI can undergo restructuring with the participation of freshly deposited metallic Li to form low-oxidation-state species with highly amorphous and heterogeneous structure.