Spectroscopic studies on the mechanism of liquid formation and ionic conductivity in the LiCF3SO3/acetamide complex system

A molten salt electrolyte composed of lithium triflate (LiCF3SO3) and acetamide (CH3CONH2) has been prepared and characterized by IR, Raman spectroscopy and ac impedance. It is interesting that although both lithium triflate and acetamide are solid, their mixture is a liquid in an appropriate molar ratio range at room temperature. The IR and Raman spectroscopic studies show that the Li+ ions coordinate with the CO group of acetamide while the SO3 group of CF3SO3− anions interacts with the NH2 group of acetamide via hydrogen bonding. Such interactions lead to the breakage of the hydrogen bonds between acetamide molecules and the weakening the Coulombic interaction between the anions and cations of lithium triflate, resulting in the formation of the molten salt. The behavior of ionic transport obeys well the empirical Vogel-Tammann-Fulcher (VTF) type relationship for the molten salt electrolyte. The ionic conductivities of the LiCF3SO3/acetamide complex with different molar ratios depend strongly on the ionic species in the complex system. Among them, the complex at a molar ratio of 1:5 shows the highest ionic conductivity due to the relatively high amount of “free” ions at room temperature.