Facile preparation of deep eutectic solvents having high electrical conductivities

•A facile preparation of deep eutectic solvents (DESs) composed of various imidazolium iodides and I2 was demonstrated.•The DESs show high electrical conductivities (e.g., ~70 mS cm−1 in 1:4 mixture of 1-ethyl-3-methylimidazolium iodide and I2).•The molar conductivity of a DES in this study was much higher than the ideal value based on the Walden rule and viscosity.•Raman spectra showed polyiodides in mixtures of 1-hexyl-3-methylimidazolium iodide and I2.High electrical conductivity is accounted for by the Grotthuss mechanism.