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/LiAsF₆ 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 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.