Influence of Water Content on the Surface Morphology of Zinc Deposited from EMImOTf/Water Mixtures

Due to its low cost, high abundance and non-toxicity zinc metal is a very promising electrode material for rechargeable batteries. The main drawback of using zinc in aqueous alkaline solutions is the formation of zinc dendrites, which lead to cell failure, and a low coulombic efficiency. In this study the suppression of dendritic zinc growth by applying either pure 1-ethylimidazolium trifluoromethane sulfonate or 1-ethylimidazolium trifluoromethane sulfonate / water mixtures with zinc trifluoromethane sulfonate as electrolyte formulations was examined. The surface morphology of the deposited zinc is significantly influenced by the amount of water present in the electrolyte. Cyclic voltammetry measurements showed a less negative reduction potential of zinc with increasing water content. Additionally, the presence of air in the electrolyte proved to be another factor influencing the cyclic voltammetry results. Furthermore, galvanostatic cycling data showed a lowering of the overpotential and constant potentials during long-term cycling of 100 cycles if water is present in the electrolyte, and SEM micrographs confirmed that the surface structure remains compact even after long-term cycling.