Topography images for samples kept at 2.4 V and from a dry (reference) electrolyte are shown in SI-3, where little to no features were observed. At 1.7 V the surface is seeded with particles of ~10s of nm in height and ~50-100 nm in width. At lower potentials the most notable feature are islands of a few micron wide, but only ~3 nm high, that show a remarkable similarity to so-called 'micropancakes', typically associated with trapped gas in a liquid environment .