Fig. 3.

SEM characterization of the deposited Li film on the Li/Cu substrates. A–E are top-view SEM images of the deposited Li films on the Li/Cu substrates (50-µm-thick Li, 15-µm-thick Cu) in 1 M LiPF₆ EC-DMC (EL-0), 1 M LiPF₆ FEC-DMC (EL-1), 1 M LiPF₆ DFEC-DMC (EL-2), 1 M LiPF₆ CF₃EC-DMC (EL-3), and 1 M LiPF₆ FEC-DMC + DTD (EL-4), respectively. The Li films were deposited in LiCoO₂-Li cells by charging at 0.1 C to 4.5 V vs. Li⁺/Li. The same amount of Li (∼4.2 mAh cm⁻²) was deposited for all five cases. Microsized Li particles were observed in EL-0, -1, and -4. Smaller particles were observed in EL-3. F–J are the corresponding cross-sectional SEM images. The thickness of the deposited Li layer increases in the order of EL-1, EL-4, EL-2, EL-0, and EL-3.