Generation of Na on anode. SEM images of (a) pristine Super P/Al anode and (b) the Super P/Al anode after charging to 1 mAh with Na coated on the surface. The insets in (a) and (b) are the corresponding photographs of the anode. (c) XRD patterns of Super P/Al anode before and after charge. (d) Schematic diagram of in situ optical microscope setup in liquid electrolyte. (e) In situ optical images for the process of Na formation. (f) AFM images of Na deposition on Au electrode at the time of 0 s and 2040 s. Scale bar: 40 μm.