Fig. 5. Ex situ interface characterizations of cycled Li metal electrodes.

a–f Top-view and cross-sectional SEM images of plated Li metal on Cu foil after 5 cycles at 0.5 mA cm⁻² with a cutoff capacity of 5 mAh cm⁻² at 30 °C, including BFE (a, d), DME (b, e), and DEE (c, f). g–i Cryo-TEM (g), and IFFT (h, i) images of cycled Li metal on Cu grid in BFE electrolyte (the Li metal was plated on the Cu grid via Li | |Cu cells through electrochemical deposition). j F1s XPS spectra with etching depth profiles of the cycled Li metals in different electrolytes (BFE, DME, and DEE). The Li||Cu cells were cycled at 0.5 mA cm⁻² with a cutoff capacity of 5 mAh cm⁻² at 30 °C for 5 cycles before the XPS measurements. All tests were performed using coin cells.