Morphological studies of Li deposition processes in LiAsF6/PC solutions by in situ atomic force microscopy

The morphology of Li deposition-dissolution processes in propylene carbonate/LiAsF5 solutions was studied using in situ atomic force microscopy (AFM). Dry (20 to 30 ppm of water), water contaminated (200 ppm H2O), and CO2 saturated solutions were tested. The substrates included copper foils, which are currently used as current collectors for Li electrodes and metallic Lithium. The morphology of Li deposition in dry LiAsF6 is compared with that observed in LiClO4 and LiPF6 solutions. Basically, the morphology of Li deposition in LiAsF6 solutions is much smoother than in LiClO4 or LiPF6 solutions. The presence of water in solutions roughens the morphology of both the surface films formed on copper at low potentials and the Li layers deposited. The correlation between the previously known properties of the Li-solution interphase in these solutions and the present morphological observations is discussed. The results thus obtained further demonstrate the applicability of AFM for in situ morphological studies of highly reactive electrode surfaces.