Diluents composed of H2O and dimethyl sulfoxide (DMSO) were added to 1-ethyl-3-methylimmidazolium dicyanamide (EMI-DCA), yielding an electrolyte system that is potentially applicable for Zn–air batteries. H2O is critical for enhancing both the electrolyte conductivity and Zn/Zn(II) redox kinetics, but impairs Zn/Zn(II) redox reversibility and cyclability. DMSO has the ability to stabilize the electrolyte from H2O decomposition and is beneficial for maintaining Zn/Zn(II) redox reversibility and cyclability. Improved Zn/Zn(II) redox kinetics and reversibility, together with good cyclability up to 200 cycles, was achieved in EMI-DCA + H2O + DMSO in a mole ratio of 1:1.1:2.3.