Figure 4: Morphology of Li-metal anode during plating/stripping.

Top view SEM images of (a) pristine 3D porous Cu foil without Li metal and after plating (b) 0.5 mA h cm⁻², (c) 1 mA h cm⁻² and (d) 2 mA h cm⁻² of Li metal into 3D current collectors; anodes after stripping (e) 1 mA h cm⁻², (f) 1.5 mA h cm⁻² and (g) 2 mA h cm⁻² (that is, recharged to 0.5 V) from the Li anodes (2 mA h cm⁻²) with 3D current collectors. (h) Side view SEM image of the Li anode with the 3D current collector after 10 cycles. Scale bars, 2 μm. The rectangle symbols exhibit the amount of Li metal in each image; each solid rectangle represents 0.5 mA h cm⁻² of Li. The Li plating/stripping states (a–h) are indicated in (i) galvanostatic discharge/charge voltage profile at 0.5 mA cm⁻². Note that due to the nature of the ex situ method, the profile is only an indication for the Li plating/stripping states in a–h, and is not necessarily the real test result of each sample.