Fig. 5

Morphology and solid-electrolyte interphase (SEI) probing of the plated Na in buffered Na–Cl–IL electrolyte. a–d High-resolution XPS spectra for Na Auger and O1s (a), F 1s (b), Al 2p (c) and Cl 2p (d) of the Na negative electrode from a Na/NVP@rGO cell with NVP@rGO mass loading of 5.0 mg cm⁻² at different depths, respectively. The cell was cycled at 100 mA g⁻¹ (~0.5 mA cm⁻²) for 20 cycles and stopped at fully charged state prior to characterization. e Cryo-TEM image of Na-plated Cu grid at a current density of 0.1 mA cm⁻². Scale bar, 500 nm. f, g High-resolution Cryo-TEM images and diffraction patterns (inset) of SEI concerning Al₂O₃ and NaCl. Scale bars in (f, g), 5 nm. h High-angle annular dark-field (HAADF) and the corresponding element mapping images for SEI composition probing using STEM. Scale bar, 100 nm