Lithium electrodeposition experiments were carried out in a 3-electrode cell, using a copper substrate as working electrode (150 nm copper + 10 nm titanium sputtered on a silicon wafer, Si-Mat), and metallic lithium as counter-, and quasi-reference electrode (QRE). All potentials in the remainder of the text are versus the Li QRE. We use tetraethylene glycol dimethyl ether (4G) as a solvent, which was selected mainly based on the high boiling point and the electrochemical stability of ether solvents . The solvent was dried over 4 Å molecular sieves, after which 1 M LiTFSI and 1 M LiClO4 electrolytes are prepared with varying amounts of water as additive.