Superconductive rhenium films were electrodeposited from a water-in-salt type electrolyte with superhigh concentration of LiCl. Rhenium free electrolytes were also studied with linear sweep voltammetry to further understand the effects of LiCl salt concentration on the ion activity and side reactions. The morphology, crystallographic structures and superconductivity of the electrodeposited Re films were characterized. The hydration of LiCl resulted in a depletion of free water molecules and a

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... crease of proton reduction. While cracks were ubiquitously observed in films electrodeposited from traditional electrolyte, such cracks are eliminated when water-in-salt is used. An increased critical temperature of 6 K with an improved stability was observed for the Re film deposited from this new type of electrolyte.