Fig. 3: Characterization of SEI on the Li metal surface.

In-depth C 1s XPS spectra of Li metal anodes after 20 cycles in a Blank, b F6, and c F6L. In-depth F 1s XPS spectra of Li metal anodes after 20 cycles in d Blank, e F6, and f F6L. g TOF-SIMS depth profiles of SEIs formed in Blank, F6, and F6L. Cryo-TEM images of SEIs formed in h Blank, i F6, and j F6L. Source data are provided as a Source Data file.