Fig. 5.

SEI chemistry and the charge transfer process. a The atomic fractions of C, O, F, and Na as a function of SEI depth, calculated from the XPS spectra depth profiling (Supplementary Figure 19). b Schematic of the SEI compositions formed in different electrolytes and a comparison of the charge transfer energy barriers. [Na⁺] means that the Na⁺ may be solvated. There is a smaller amount of organic species in the SEI formed in the diglyme-based electrolyte and the inner part of the SEI is mainly composed of inorganic species. c XPS C 1s spectrum before etching in the EC/DEC-based electrolyte. d XPS C 1s spectrum before etching in the diglyme-based electrolyte