a The schematic operando neutron depth profile (NDP) setup. b Depth profiles during Li metal plating/stripping on a Cu working electrode cycled at a current density of 1 mA cm–2 to a capacity of 1 mAh cm–2 of c 1 M LiTFSI-FEC/FDMA and f 1 M LiPF6-EC/DMC electrolytes. Evolution of Li+ plating/stripping density vs. time from operando NDP during the first cycle at 1 mAh cm–2 in Li||Cu pouch cells for d 1 M LiTFSI-FEC/FDMA and g 1 M LiPF6-EC/DMC electrolytes. The depth is calculated starting from the inner surface of the Cu current collector. Evolution of Li+ plating/stripping activity for e 1 M LiTFSI-FEC/FDMA and h 1 M LiPF6-EC/DMC electrolytes, which is obtained from the change in Li+ density upon each time step of d and g, respectively. The color scale in NDP measurements indicates the local Li concentration in mol/liter. i and j Schematic representation of the plating/stripping mechanism in the two electrolytes.