a, b Scanning electron microscopy (SEM) images after Li plating at current density of 1 mA cm−2 to the capacity of 1 mAh cm−2 on a Cu substrate in 1 M LiPF6-EC/DMC and 1 M LiTFSI-FEC/FDMA. c, d In situ optical microscopy images showing the cross-section of Li electrode upon plating/stripping in a symmetric cell at 1 mA cm−2, recorded at the specified plating/stripping stage in a 1 M LiPF6-EC/DMC and 1 M LiTFSI-FEC/FDMA electrolytes. The scale bar for c, d is 200 μm. e The evolution of thickness for the deposition of during Li plating/stripping. Three locations, at 1/4, 1/2, and 3/4 along the Li-metal foil are chosen to measure the change in thickness, from which the average thickness is calculated.