Fig. 5

Microscopy images of fully charged amorphous Si anode films. a–d FE-SEM cross-sectional images of a, c non-porous and b, d porous films. Scale bars represent 10 µm. In order to clarify the anode films’ cross-sections, EDS elemental mapping images for Si are overlaid on the corresponding FE-SEM images in (c) and (d). e, f High-magnification images of e non-porous and f porous films. Scale bars represent 1 µm. The cross-sectional FE-SEM images were taken at a tilt angle of 60°, and thus the scale bar in the images is only applicable to the horizontal direction. The upper and lower dashed white lines in (e) and (f) indicate the surfaces of amorphous Si films and stainless-steel substrates, respectively. The carbon top layers onto the Si films in the figures are protection layers against damage from FIB. Inset in (f) shows higher-magnification image and the white arrows in the inset indicate representative shrunk pores in the fully charged porous Si film. The areal mass loadings of the as-prepared non-porous and porous films were 0.23 mg cm⁻², and the thicknesses of these films were 1.00 and 1.55 µm, respectively. The anode films were cycled with a current density of 0.1 mA cm⁻² in the voltage range of 0.01–1.2 V vs. Li⁺/Li (see Supplementary Fig. 5 for galvanostatic charging/discharging potential profiles of the anode films) and subsequently the solid-state electrochemical cells were disassembled at lithiated state after 6th charging in an Ar-filled glove box. The thicknesses of the fully charged non-porous and porous films were 2.97 and 3.38 µm, respectively