Fig. 4: Optical microscopy and SEM investigation of Li/Li₂₂Sn₅ electrode.

a In situ optical microscopy investigation of the interfaces between the electrolyte and electrode for the Li|Li (up) and Li/Li₂₂Sn₅|Li/Li₂₂Sn₅ (down) symmetric cells during lithium plating process (1 mA cm⁻², 10 mAh cm⁻²) (scale bar, 300 μm). b Top view SEM images of Li foil (left) and Li/Li₂₂Sn₅ foil (right) after a stripping/plating cycle with 5 mAh cm⁻² of lithium under 5 mA cm⁻² (scale bar, 1 μm). c–e Cross-sectional SEM images of a Li/Li₂₂Sn₅ foil before electrochemical lithium stripping/plating cycling (c), after stripping 10 mAh cm⁻² of lithium under 5 mA cm⁻² (d), and after a stripping/plating cycle with 10 mAh cm⁻² of lithium under 5 mA cm⁻² (e) (scale bar, 200 μm). f, g Cross-sectional SEM images and the corresponding EDX mapping images of a Li foil (f) and a Li/Li₂₂Sn₅ foil (g) after 50 stripping/plating cycles with 5 mAh cm⁻² of lithium under 5 mA cm⁻² (scale bar, 50 μm).